Had to keep it under 100 sq ft do to being in a historic district but you get the idea. Turn the 2x4's in the walls flat,this gives room to butt the windows against one another with a clean look,.Pre paint/stain all the wood before construction is a huge timesaver.
I built one a few yrs ago,used eggrock for the floor to trap heat and release over night. Went with a clear poly type roof ,sink,2 small exhaust fans. I will post some pics
I use the outdoor germicidal bleach and run it thru my chemical injector .spray/wait 5/rinse,repeat on tough stuff. Wet anything you are worried about prior to bleaching and rinse well after. (including injector)Works better than anything i have found and cheap.