Depends how you want to display stuff. For G1, I'd think having a shelf at the bottom for huge guys would work, but most of the rest of "large" figures would be around combiner height, so that'd be a factor. Same with Generations, shelves with Leader class or combiners will need basically that much space.
Have you considered floating shelves along the upper part of the room, where you don't have normal shelving?
My shelves are around 9" deep and can snugly but comfortably display roughly 3 layers of figures. Unless you're using risers and lighting setups I worry 11.5" might be a bit deep for most displays. I guess it depends how tightly you want to pack them!
Don't forget to plan a bit of extra space if you can for collection growth! I do purges regularly but expansion can still occur.
