You don't need an architect, designer, or anything like that. You need a credible builder. I can recommend Dimetri Homes & Remodeling.
They have done this kind of thing hundreds of times and have an excellent reputation in Sumter and Marion Counties.
They can do it all, and their work is impeccable.
Don't hesitate to give them a call and speak with them. You won't be sorry.
Demetri Homes and Remodeling
8311 SE Highway 42, Summerfield, FL 34491-7075
Demetri Homes & Remodeling - The Villages, FL
(352) 427-2787