I thought it was really easy. The hardest bit is cutting the hole, but you'd have to do that anyway even if you were doing a door. The hole doesn't have to be too exact (only enough to make sure that it doesn't jam on the flap as it opens), because the frame of the flap covers over any dodgy bits, and you literally put half the flap on the outside, half on the inside, and screw them together with the screws provided. It sandwiches to itself with the wood inbetween so no need to even drill holes for the screws.