Room modes and angled walls?

My drum room will be 7ft h x 10.5ft w x 17.5ft l. According to the ModeCalc these are the best dimensions for the space I have, ratio = 1:1.50:2.50 My question is...how much do I offset the walls to get the best acoustics? The space I have to make the room is 7'h x 12.5'w x 18' l. Thanks

i'd skip hard angled walls and use rectangular spaces and build out treatment walls for trapping, slats, etc.