12 birds. He's gonna need 48 s.f. MINIMUM in the coop, and 120 s.f. of run space, and a minimum of 5 s.f. of ventilation. If he skimps in this area, he will be setting himself up for problems with air quality, aggression which can lead up to blood shed and cannibalism, increased likelihood of disease and parasites due to crowding stress.
A shed style coop can be easily built. A cattle panel coop would be even easier to build. Check out the Wood's open air style coop. And check out Sunset Sheds and Garages. Sunset puts out a number of little books that make it possible for the "newbie" to understand how to successfully put a sturdy custom designed building together.
IMO, pre fab coops are junk. Falsely advertised, designed by folks who are clueless regarding the needs of a chicken or the poultry owner.