You're going to cut the ailerons out of the wing. In order to avoid having to measure anything, this is what I did: When you pull the wing up off the building board, before you sheet the opposite side, make pin holes next to the aileron spars and the doubler on the inboard portion of the wing. Once the wing is sheeted completely, transfer the pin holes to the opposite side and then cut the ailerons.

Also, when I was sheeting the wing, I used super glue on the wing ribs, but used wood glue on the skin butt joints for easier sanding. Consider using square stock to reinforce the aileron servo cut outs as well.