Builder fee for building a duplex of 5000 sqft

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Hello

I am in the process of finding a builder for a duplex construction in jefferson park area in Denver. Duplex is 5000 sqft and perhaps basement of 1000 sqft. So far, 3 Builders have quoted 12-14% of the cost to build as their fee (+supervision fee ). Two builders have quoted a flat fee of 80-100k for the project (+supervision fee).

I am leaning towards flat fee builders. Tpically, what is the builder fee for this size project?

Thank you