Savageayape,
I agree with 14 foot tall at a minimum. Everybody thought I was crazy going that tall on my 40 x 60, till my father-in-law wanted to put his motor home with roof mounted air inside.....
2nd thing - like you, to save money when I built mine, I only put in sliding doors. I wish I had put one normal or slightly larger than normal garage door in mine, off set from the sliders. It really stinks to have to move a (heavy) 16 wide 14 tall slider to get the lawn mower or a four wheeler out. Plus, you can add an opener if you ever get to the point of storing a routinely driven vehicle in the barn. We keep our convertible in our building, and a lot of times I might drive it if I did not have to open the door, pull the car out, get out and close the door, then repeat process when you get back home.....
If you don't want to spend the money to put the door in now, just lay out your sliders and storage arrangement to plan for the garage door, and have the builder rough in the support poles at the correct spot to allow framing, cutting out the metal, and installing a roll up garage door later. I really wish I had done that.
Been there, done that, trying to work arount it now......