Bump out room on to covered porch.

My house has a 6' front porch with the roof trusses overhanging the entire span. I want to bump out a bedroom 4' (keeping the 2' eave overhang to be consistent with the rest of the house. The span would be 12', and would have a double w Adding the walls is easy, and the heat is a non issue as it is hot water heat. My question is could I remove the deck boards and put down plywood, then add a bottom layer of plywood and insulate the floor cavity. The goal would be to use the existing footing, etc. The total add would be under 50sf. Thoughts? The room is on the bottom rh corner of the image.