1. Go to edit town
2. Pick a house that your sims want but can't afford
3. Set it to public lot
4. Make your sims stay there all the time
The problem with that is of course anyone else can stay there as well!
If you do want to use cheats solely for the acquisition of a set house,
type CTRL + SHIFT + C, type TestingCheatsEnabled True, then type FamilyFunds X Y,
where X= name of family and Y= monetary amount.
Simply add the cost of the house to whatever is the current funds the family has, and bingo, they have enough to buy the house and nothing else - which feels a lot less like cheating than Motherlode does!
Yeah I knew about that but I thought this was pretty cool and wanted to point it out