I use solidworks.... cracked for personal use.
I know, I know... it ain't FOSS, but man it works really well and I have several industry standard certifications for it.
I have a fully fleshed out model of my house, and as I design things, I spacecheck to ensure a good for, and a good aesthetic. then I build the thing, and put it where I designed it to go.
it -did- help that I had the original architectural drawings, xD
only took.... I wanna say, 4 hours(?) to get it all imported :D