Exhibit 10.1

AMENDMENT NO. 1 TO STOCK PURCHASE AGREEMENT

THIS AMENDMENT NO. 1 TO STOCK PURCHASE AGREEMENT (the “Agreement”), dated as of
April 7, 2006, is entered into by and among NCI Building Systems, Inc., a
Delaware corporation (“NCI”), The Heico Companies, L.L.C., a Delaware limited
liability company (“THC”), and Robertson-Ceco Corporation, a Delaware
corporation (“RCC”).

RECITALS

WHEREAS, NCI, THC and RCC are parties to that certain Stock Purchase Agreement
dated as of February 21, 2006 (the “Purchase Agreement”);

WHEREAS, capitalized terms used herein, unless otherwise herein defined, are
used with the meanings given them in the Purchase Agreement, and NCI, THC and
RCC are sometimes referred to herein collectively as the “Parties” and
individually as a “Party”;

WHEREAS, the Parties desire to modify the working capital base used for the
purposes of the definitions of Negative Working Capital Adjustment and Positive
Working Capital Adjustment;

WHEREAS, NCI desires that the Company retain at and after the Closing the
following agreements and Indebtedness in respect of such agreements: (i) Lease
Agreement between The Industrial Development Board of Carter County, Tennessee
and Robertson-Ceco Corporation dated January 1, 2000 and all related
instruments, documents and agreements and the related Indebtedness thereto (the
“IRB”), and (ii) the capital leases listed on Schedule A attached hereto (the
“Cap Leases”);

WHEREAS, the Parties desire to amend the Purchase Agreement (i) to reflect an
adjustment to the Acquisition Consideration in respect of the IRB and Cap
Leases, (ii) to waive RCC’s obligation to endeavor to pay off the IRB and Cap
Leases prior to Closing, and (iii) to waive RCC’s obligation to deliver pay-off
and release letters for the IRB and Cap Leases to NCI at the Closing;

NOW, THEREFORE, in consideration of the foregoing recitals and of the mutual
promises set forth herein, the parties hereto hereby agree as follows:

1. Amendments to Definitions.

(a) The definition of “Negative Working Capital Adjustment” in the Purchase
Agreement is hereby revised and amended by replacing “$42,896,000.00” with “the
Year End Working Capital”.

(b) The definition of “Positive Working Capital Adjustment” in the Purchase
Agreement is hereby revised and amended by replacing “$42,896,000.00” with “the
Year End Working Capital”.

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(c) Item (viii) of the definition of “Permitted Liens” in the Purchase Agreement
is hereby revised and amended to add the phrase “and Liens in connection with
the IRB and/or Cap Leases” immediately after the last word in such item (viii).

(d) The Purchase Agreement is hereby revised and amended to restate clause
(A) of the definition of “Purchase Date Working Capital” in its entirety as
follows:

“(A) Purchase Date Working Capital shall not include any liabilities or debt
issuance costs in respect of the Indebtedness Amount;”

(e) The Purchase Agreement is hereby revised and amended to insert the following
sentence immediately after the last sentence in the definition of “Purchase Date
Working Capital” in Section 1.1 of the Purchase Agreement: “Except as set forth
in clause (C) of this definition, Purchase Date Working Capital shall be
calculated in accordance with the same principles used in the preparation of the
Year-End Working Capital.”

(f) The Purchase Agreement is hereby revised and amended to replace in its
entirety the definition of “Purchase Date Balance Sheet” in Section 1.1 of the
Purchase Agreement with the following: ““The Purchase Date Balance Sheet” means
a consolidated balance sheet of the Company as of the Closing Date which is
prepared in accordance with the same principles used in the preparation of the
Year-End Balance Sheet and in accordance with generally accepted accounting
principles consistently applied.”

(g) The Purchase Agreement is hereby revised and amended to insert the following
definition immediately after the definition of “Investigation” in Section 1.1 of
the Purchase Agreement: ““IRB” has the meaning specified in Amendment No. 1 to
this Agreement.”

(h) The Purchase Agreement is hereby revised and amended to insert the following
definition immediately after the definition of “Assumed Liabilities” in Section
1.1 of the Purchase Agreement: ““Cap Leases” has the meaning specified in
Amendment No. 1 to this Agreement.”

(i) The Purchase Agreement is hereby revised and amended to insert the following
definitions immediately after the definition of “Wholly Owned Subsidiary” in
Section 1.1 of the Purchase Agreement:

 

  (i) ““Year-End Balance Sheet” means the audited consolidated balance sheet of
the Company as of December 31, 2005 which is prepared in accordance with
generally accepted accounting principles consistently applied.”

 

  (ii) ““Year-End Working Capital” means, as determined from the Year-End
Balance Sheet, the amount by which (i) the sum, without duplication of

 

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amounts, of all amounts that are included and classified as current assets on
that balance sheet and that are included in the Acquired Assets exceeds, or is
exceeded by, (ii) the sum, without duplication of amounts, of all amounts that
are included and classified as current liabilities on that balance sheet (other
than current maturities of long-term debt) and that are included in the Acquired
Liabilities; provided, that (A) Year-End Working Capital shall not include any
liabilities or debt issuance costs in respect of the Indebtedness Amount; (B)
Year-End Working Capital shall be calculated without regard for any LIFO
inventory reserves; and (C) if those current assets are exceeded by those
current liabilities, Year-End Working Capital will be expressed as a negative
amount.”

2. Amendment to Section 2.2.

(a) Section 2.2 of the Purchase Agreement is hereby amended and restated in its
entirety to read as follows:

“Section 2.2 Acquisition Consideration. NCI shall pay to RCC as payment for the
Company Capital Stock, an amount equal to $370,000,000, less the outstanding
Indebtedness under the IRB as of the Closing Date, less the outstanding
Indebtedness under the Cap Leases as of the Closing Date, plus $47,933.20 in
respect of the HS Batten Lok expenditure (the “Acquisition Consideration”), to
be paid by wire transfer on the Closing Date in accordance with the
instructions, if any, that RCC will have delivered to NCI. The Acquisition
Consideration is subject to adjustment pursuant to Section 8.3.”

3. Amendments to Section 6.7.

(a) The first sentence of Section 6.7 of the Purchase Agreement is hereby
amended and restated in its entirety to read as follows:

“Prior to or at the Closing, the Company and RCC shall ensure that neither the
Company nor any of its Subsidiaries has any outstanding Indebtedness for
borrowed money, except for any Indebtedness outstanding under the IRB and Cap
Leases.”

4. Amendments to Section 7.3(c)(8).

(a) Section 7.3(c)(8) is hereby amended and restated in its entirety to read as
follows:

“evidence reasonably satisfactory to NCI that all Indebtedness for borrowed
money of the Company, except for any Indebtedness outstanding under the IRB and
Cap Leases, has been, or at the Closing will be, repaid in full and that the
Company and its

 

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Subsidiaries have been fully and unconditionally released from all obligations
and liabilities thereunder, except with respect to the IRB and Cap Leases; and “

5. Amendments to Section 8.3. The first sentence of Section 8.3 is hereby
amended and restated in its entirety to read as follows:

“As soon as practicable, and in any event on or prior to the later of the 90th
day after the Closing Date and the 60th day after NCI receives the Year-End
Balance Sheet, NCI will cause to be prepared in writing and delivered to RCC (i)
the Purchase Date Balance Sheet and (ii) a Post-closing Statement.”

6. Release. NCI hereby irrevocably waives, releases and discharges forever THC,
RCC and their payment obligations in connection with the IRB and Cap Leases, and
NCI hereby covenants and agrees that it will not, directly or indirectly, seek
to recover any amounts in connection such payment obligations from any of THC,
RCC and their successors and assigns.

7. General Provisions.

(a) Except as expressly amended, modified, agreed, waived, released or settled
herein, including without limitation in the recitals hereto, the Purchase
Agreement shall remain unchanged and in full force and effect, and as amended or
modified herein, the Purchase Agreement is hereby ratified, approved and
confirmed in all respects.

(b) After the date hereof all references in the Purchase Agreement to the
“Agreement,” “herein,” “hereof” and the like, shall refer to the Purchase
Agreement as amended or modified herein.

(c) This Agreement may be executed in multiple counterparts, each of which shall
be deemed an original, but all of which together shall constitute one and the
same instrument. Any counterpart may be executed by facsimile signature and such
facsimile signature shall be deemed an original.

[SIGNATURE PAGE FOLLOWS]

 

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IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of the
date first above written.

 

NCI BUILDING SYSTEMS, INC. By:  

/s/ Norman C. Chambers

Name:   Norman C. Chambers Title:   President and Chief Operating Officer
ROBERTSON-CECO CORPORATION By:  

/s/ Lawrence G. Wolski

Name:   Lawrence G. Wolski Title:   Vice President THE HEICO COMPANIES, L.L.C.
By:  

/s/ Lawrence G. Wolski

Name:   Lawrence G. Wolski Title:   Vice President

[Signature Page to Amendment No.1 to Stock Purchase Agreement]

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Schedule A

IOS Capital Agreement

KIP American, Inc. Agreement