Absolute minimum incl assembly is 40' 6" long (6" is space to attach the bag at the end of the mould, would mean climbing under it to get to the other side),  14'6" width (assembled width of the lee hull and cabin, plus 1' each side to get around it), 8' high to allow you space to sand and apply paint to the cabin roof. 

The absolute minimum to infuse the components depends on how small you want to make each one and how many joins.  If the lee hull was built in 4 lengths (8 pieces) and the roof in 2, you could do the infusing in a single car garage, 11' long.  It would take a lot longer (multiple infusions and jigging to get the pieces aligned), cost and weigh a little more.  

My advice would be to buy a cheap pump from Ebay, some materials and a sheet of window glass,  do a couple of infusions to see what is involved, then build the rudders, bulkheads, booms, furniture and rudder cases in your garage.   You will then know enough to decide how much space you need, how many joins are acceptable to you and how long you will need to hire space to do the big infusions, assemble and paint it and fit it out.