Has anyone BRRRR'd an extra unit on their property?

[Landon Rasmussen]

I'm closing on a 3 unit property in a couple weeks. The attic of the property is massive and easily large enough for a 4th unit.

My idea is this: At some point in the near future I'd like to add that 4th unit. My brother has around 30k to invest and he wants to help me out. If I can get this 4th unit built for somewhere between 20-30k (which I believe I can), I'd like to get a tenant in there for 800-1000 a month, then get a HELOC and use that money to pay my brother back in part or in full. (Timeline is to have the unit done and tenant in by the 6 month mark).

The problem is that I'm not exactly sure how much the property will appraise for post reno and or if I can even get a HELOC on the property right after purchasing.

Has anyone had any experience with anything like this?