I tryed this...
Go to build a room
Make the room as big as it can go
Then hold on to the top button tell your phones off
Then turn it on again
Go back to your sims home and those rooms work (i tryed it)

Hat's what i do, then you sell the room and you get quite abit of profit

I don't think it works anymore. I recently got sims 3 ambitions and then i tried this but
after i turn off the phone, the rooms are not there anymore. So i'm sure it won't work
anymore

Like, i tried the thing with the room. And it worked perfectly. If u do it tons of times
it may not work occasionally like i do. Sometimes it doesn't. Sometimes it does.

You make a room as big as you want it (the bigger it is the more money) then you turn your
device off fully off, don't press the tick to finish building though. Then go back on the
game the rooms will be there. Then you delete the rooms and you press the tick and you
have money!!

Thank you :)