The meter combo IS the main service panel. The panel on the inside will be a 'sub' panel; assuming it is fed from a breaker in the outside panel. And don't forget to pull a ground too.
I'd still use another main panel inside though.
Design-Build isn't supposed to mean design *as* you build.
I doubt that I'd install a main in the sub panel since it is within the same building. Still, those panel packages that come with a main PLUS a selection of breakers are sometimes less expensive than buying a MLO panel and the same breakers that come with the package. Kind of hard to argue at that point.
A 100 amp MB panel with five SP 20 amp breakers (Square D Homeline) is only $60.00. In that case, the customers are getting a main breaker whether they need it or not.