First Pop Top - Help!

[Phil Christie]

Looking for a little advice...

My partners and I are new. We've been on our REI journey for a couple years now and have done one flip successfully. We just bought a property that ARV merits a pop top. When we purchased the property we looked at numbers based on a standard flip and accounted for proportionate expense for the addition and they looked good. Now that we have been learning more about the process for a pop top, and getting GC bids back the numbers are looking like the job is a loss.

What are we doing wrong?

I'm happy to share more details.  Just looking for some help before we ditch a project that looked promising, or worse, lose money on the deal.