So far I had only 3 houses, though I'm playing from June 2009! My first one, which was a household for my legacy family, the Tysons, had museum/trophy room, 6-7 bedrooms, 2 kitchens, 3 bathrooms, a big garden, pool, office, skill room and 2 living rooms. Whole thing costed somewhere in between 1 Million - 1,3 Million simoleons. This is my second expensive household, but the worst design in my opinion
Unfortunately, my saved game vanished once I changed my operating system...
After this I built my second house in June 2010. This one had first 4 levels, and then 3 bonus levels underground. This one was pretty big and costed 1,7 Million! This is mainly because I like keeping cut gems in my houses to increase the value of the house and the quality of the room (I mean the moodlet sims get while in a particular room). Unfortunately, this one was destroyed because of my mods. At last, the latest but not the last house I've built is only 1,5 weeks old in real timing and 9 sim weeks old in game timing. Though this one is pretty young, it already costs 1 Million simoleons, has a big living room/open kitchen, enormous bedroom, with a big bathroom attached to it, my garage for 4 autos, each of which costs at least 40.000 simoleons, an underground nectary or whatever they call it, and of course the museum, which consists of gems of every type from the base game, WA and AMB, plus 9 tiberiums, each of which costs 40.000 simoleons! The next and last floor is a skill room, where my sim paints, sculpts, invents, gets tattoos and make-up, and finally travels in time! If you don't believe me I can show you the pictures of the third, but not the first and second households I've described!
(Post edited by Schipperke to remove names of mods)