In April 2013, after several dozens hours of extensive studying of Sims behavior on 3 experimental houses made by me, using two families of 2 and 8 sims, plus the pre-made ones, I made my first (final) house in The Sims 3.
I hate The Sims 3 lot sizes, for being too big. Look at this, I used the smallest standard-sized lot available in game (20×30) to build an oversized house with 258 square meters for 6 Sims (with possibility to add 2 more beds), 3 bedrooms, 3 bathrooms, carpark for 2 cars, pool, BBQ, etc. I say oversized because 6 Sims normally need 200 squares.
Error: the two doorways near staircase may appear half-walled, I placed using the cheat “moveobjects on”, because of The Sims 3 limitations, this was working well in The Sims 2.
Lot size: 20×30.
Lot price: about $170.000.
House size: 16×12.
Floor area: 258 squares + 35 squares of terraces + 8 squares of void.
Expansions required: none, The Sims 3 base game only.