Cost to replace a flat roof in Chicago about 1350sqft?

[Byron W.]

I had a roofer come by in December to fix a leak and it appears the leak is back. They gave me a 1 year warranty but when I spoke with the guy on the phone, he was making it seems like he did all he can do and my only options are a replacement. I'm going to see if I can still get him to fix it since it's supposedly covered under a one year warranty and it's leaking in the same exact spot as before.

My question is, what's a reasonable cost for replacing a flat roof of this size? It's a 3 unit building, about 1350sqft. I was told somewhere in the realm of $10k. Any help is appreciated, thanks!