The top bar is what I started with. I took a 2 X 4 cut it at an angle then turned it over and cut the other side. Then notched out for spot to set on top of hive body. I had a cut out so I built sides and a bottom to make the frame where it would be easier to attach the comb. I cut the notch a little more and at an angle, didn't want the comb to be over 11 inches so that is how long from bottom of top bar to inside of bottom. Had the measurements of hive, also had divider board to compare to, made the frame slightly smaller so it would go in hive stapled it together. You could just draw it out on your divider board and make it from that.
As for as working they build across the top bar, attach some to the sides of the frame, sometimes to the bottom. Being in the deep south in the summer you still need to be careful when handling the frames. If you forget and turn it on the side it may still fall out. I guess you could put in some wires or pins to help hold the comb into place even better. Hope this helps. On being gentle, mine are Cordovans, last week I pulled every frame out 1 at a time, inspected it and put it back, didn't have the first bee even fly around me. Good luck to you and your bees.