Math

1. assuming 

land is 650K.  
building cost is 150/sq ft. 
selling for 250 / sq ft

2. For a 4000 sq ft house
building costs 600K, + land 650K = 1.25 mil. 
4000 sq ft selling at 250/sqft = 1 mil. 
you are under for 0.25 mil. 

3. In fact. For a X sq ft house
(X* 250) - (X * 150) - 650K > 0
X (250-150) > 650K    
X > 6500 sq ft to be profitable. 

Good luck finding that buyer.