I've made two, one from scratch, and one using an old, worn out Alpine Designs pack.
They both had hour-glass frames, ABS for the Alpine Designs, and ALU for the one from scratch.
It was very hard on the one from scratch to get the tension on the mesh backpanel high enough. On the other one, I had the benefit of the manufacturer's design by cutting it up and using the fabric pieces as pattern pieces. The next one that I'm working on now will have a Fibraplex hub and carbon rods bowed out to the edges of the back panel, keeping it highly tensioned (I hope). If it works, it will be posted. If not, it will go into the scrap heap of history, and I will buy the lightest Osprey with a tensioned back panel that is big enough for my stuff.
These pics don't reveal much, but may be of interest:
The new one will have the same design as the second one, a Jackpack suspension with side arms, a shelf up top, a reach-up bottle pocket right behind the head, a zip open drop panel on the front under the shelf going down about half the height of the pack, and a suspended pocket for small stuff under the shelf in front of the bottle packet and accessible when the drop panel is unzipped part way. The idea is to be able to get to the small stuff quickly without having to unpack, and without having pockets sewn onto the outside of the pack. But the new one will be much lighter. The carbon rod weighs between .375 to .5 ounces per running foot, compared to close to 1.5 ounces for 5/8" O.D. ALU alloy per running foot. And it will provide the tension on the mostly mesh backpanel without having to install lots of little straps and buckles to pull the panel taut over an hourglass frame.