Is Foam Board Insulation Strong Enough To Be Placed Over Floor Joists And Then Install A Floor Over It?

I am going to be building a 10×14 shed when it warms up a bit. I plan to use it as a shed to store my lawn tractor and garden tools but i can see a time in the future where i may want to use it as an escape (i am going to run power, tv and internet to it). I can insulate walls and ceiling later but the floor is something i think is a lot easier when you are building the shed. My first thought... 

How Much Would It Cost To Build A 10′x12′ Wood Storage Shed And Then Bricked In. Should It Be Set On Concrete

I’m planning in putting in a 10′x12′ wood storage shed. I plan on having it bricked in at a later time to save money. What should the foundation be for the shed initially and how much should each part cost (storage shed, bicked in (with labor), concrete slab (if needed)). The other option is to have a 10′x12′ building built instead. How much would that cost and which...