I am more math nerd than artist and I struggle with most of the techniques unless their is some solid math or process behind them. I can do basic perspective drawing but that's because it has a method and rules to follow. For the really ncie 3d overhead perspective pieces is there a formula to determine how much smaller you make the base from the top of the walls to achieve that top down look? I understand the perspective concepts but every attempt I have made at making the walls looks awful. any ideas?