I designed a few ideas but with having two kids now never had the time to build any. One thought was to cut the bottoms from the truck bed stake hole pockets and mount in the lift arms from a popup camper and connect them to the cap on the truck to lift the whole thing up.
I also thought about cutting the top off a normal truck cap or a higher than cab one and making it lift up like a popup camper. Use standard off the shelf parts it shouldn't be too bad.
Lifting the whole top seems to be the easiest, just find lift arms that extend the height you want, then cut the bottom out of the stake pockets then put some U channel under the bed between the bed and truck frame sticking out to under the stake pockets to support the lift arms. popup camper lift arms are generally a square tube with another inside with springs to extend them, then a steel cable to pull them down, so you put the arms all 4 in place coming up theough the stake pocket holes and tie the cables together and to a winch somewhere to pull them down. Then fasten the cap to the top of the lift arms and then make up a latch system inside in place of the normal clamps that wold hold it down. Then look up a place that makes replacement popup canvas and give them the dimensions.