heh. This is the way I play with a lot of my sims. (Even if they don't love the outdoors). No rain, no mosquitoes, only reason for room(s) is for pre-moodlet manager, or people who can't use the moodlet manager (children, infants).
Only need to have wall(s) to support certainly types of plumbing (e.g. probably toilet, shower, sink), and post paintings. And note that paintings hung on OUTSIDE walls count towards "house decorated with xx paintings" count.
And yes, I build pretty houses too... but when I'm optimaxing... it's the 1-2 walls, toilet, shower, sink on other side, etc.
-Holmes