There is an old game (but one of the best in my opinion) that the levels are always random... someone remember the X-Com: Ufo Defense ?
I think they made a lot of "blocks", like, one with a big house, another with some stores, or 2 little houses, the other only with grass, and them they just randomize each of the level´s block.
There are like 10 blocks with different houses...and on the end the levels are neve the same!