On a tiny 1×2 lot I built a large, extremely fat and cubish house, completed with pool and hot tub. A good home for a family with 6 sims with a possibility to add 2 extra single beds, but there are not enough bathrooms for 8 sims.
Lot size: 1×2.
Lot facing: North.
House price: $141,521 in base game, $140,828 in Ultimate Collection, $24,785 unfurnished.
Floor area: 188 squares, excluding 4 squares of staircase void.
Pool area: 20 squares.
Expansions required: none, just base game only.
PS: I do not know how to create such small lots like 1×2. I downloaded them from ModTheSims.info (Mini residential lots by MaryLou).