It use to be on discovery. The basic premise was similar to monster garage. In this one Steve Watson, I think his name is, would get a team of folks who have worked in the construction industry and they would go to a home and the homeowner would have a theme, like one episode was Gangster house.
At the beginning of the episode they would have Steve meet with an architect or one or 2 other folks and they would talk over ideas for a few minutes. Then the building on the house would start. The home owner would turn the key over to Steve and they would live in an RV. They were not allowed to go into the house or try to look at all while the building went on. They would have 5 days to finish the project, from Monday 8 or 9am, till midnight Friday, and if they did they would win some expensive type of tools. If not, and they did fail on a few episodes, Steve would call in a team who would would finish it.
The Wikipedia (I know wikipedia is hated here but tough I"m going to put the page here anyway:
http://en.wikipedia.org/wiki/Monster_House_(TV_series)