He needs 500 * 12 = <<500*12=6000>>6000 square feet
This means it cost $5 * 6000 = $30,000
That means construction comes to $30000 * 2 = $<<30000*2=60000>>60,000
So the total cost is $60000 + $30000 = $<<60000+30000=90000>>90,000
His partner covers $90,000 * .4 = $<<90000*.4=36000>>36,000
So he has to pay $90,000 - $36,000 = $<<90000-36000=54000>>54,000
#### 54,000