Has anyone been through a garage reconversion?

[Bienes Raices]

I made an offer on an REO that has an unpermitted garage to bedroom conversion. If my offer is accepted, I want to convert it back to a garage.

The county told me that house has no current fines on it for code violations. The former owner put an unpermitted door on the side of the house to enter the garage/bedroom. The actual garage door is still intact.

The county told me I would have to get an architectural engineer to come out and do a drawing for a plan in order to remove the new door. Does anyone has an idea of how much these drawings cost? I'm not even sure who to call to find out about doing this.

Also, as the new owner, could I be liable for back property taxes based on the fact that that additional room was never assessed? The county didn't mention this on the phone but I was reading about this on the web. I don''t know what year this conversion was put in, and it looks like the previous owners got about 80% through the conversion, so the new room was probably never used.