Not worth it.

For example, at my place, even old house of 2000 sq ft is selling for 500K+.

So if you bulldoze it and build another 2000 sq ft house, at $150 / sqft, it cost you 300K.

So your total cost is 500K + 300K = 800K, and a brand new 2000 sq ft house is selling for 700-800K, you barely make even.

So you have to build a HUGE house of 4000 sq ft, it cost you 600K, your total cost is 1.1 mil, and how much can that house sell? maybe 1.5 mil.  Maybe less. 

Whole lot of trouble and money, without too much return. You can do it for your own home, it's home you want to live and the trouble is worth it.  for flipping, nope.