The main sources of funding for a small construction business are bank loans and angel investors. With regards to bank loans, banks will want to review your business plan and gain confidence that you will be able to repay your loan and interest. To acquire this confidence, the loan officer will not only want to confirm that your financials are reasonable. But they will want to see a professional plan. Such a plan will give them the confidence that you can successfully and professionally operate a business.
The second most common form of funding for a construction business is angel investors. Angel investors are wealthy individuals who will write you a check. They will either take equity in return for their funding, or, like a bank, they will give you a loan. Venture capitalists will generally not fund a construction business.