Chiefusersharps

I have a second floor that extends about 18"-24" over the first floor. I want to put a wall attached sunroom on my deck even with the first floor. Problem is I have 96 inch clearance from bottom of the 2nd floor bumpout and the top of my deck. The back wall of the sun room requires 100 inches. I guess my question is, what is likely to be under the vinyl ? Will there be a way to modify the underneath?