Only 100 K for rehab, most likely not enough

[Henri Corbusier]

Hi BP. I find myself in a situation where I seem to have a deal in Los Angeles. To make a long story short, I've helped a few fix and flip guys for a while free and finally someone said they would wholesale one of their a deals to me. At first glance it looks great. 250k purchase, ARV on something similar is around 550k. It's LA, has a view, I said yes. After getting the go ahead from a hard money lender for purchase, they say they can offer 100k for rehab. My plan was to add about 500sqft. The more I look at it though, it seems like I'll have to do more than just gut it, but redo some foundation, reframe about half the existing building, new roof, rewire, plumbing, and new everything else. Basically all new. Now I'm just stuck thinking I'm not going to be able stretch out 100k loan to get it done. I'm an architect so I have some idea of what I'm doing. But the projects I work on are 500$+ /sqft. I see some flippers building for less than 100$ sqft and can't figure that part out. I have tried to calculate materials and factor in labor but can't see how some people can build for 100$ sqft. Does anyone ever get estimates near this price? At this point I'm thinking maybe just buy it, get the design permitted, and sell it as is. Has anyone else run into similar situations?