The Bluejay kit comes with laser cut ribs with the 1/4 inch jig holes.

I just bought some poplar scant wood at the home improvement store and some 1/4 inch steel rod at the tool store. You have to be very careful to drill the holes accurately in the wood endplates. Measure it twice and rework if it's not perfect.

I had to polish the steel with some sandpaper and relieve the holes in the ribs with a 1/4 inch drill to get everything to cooperate.

You can see that I've braced the center of the steel rods so they won't sag.