It's basically two 8 foot long 1x2s with a bunch of cross pieces to hold the tires in place.
You can use 2x6's for the cross pieces and save yourself a bunch of time (cut a bunch of 24" long 2x6 sections, screw them in, done), but stores were closed to I used what I had around. I created a bunch of 6" long pieces of 2x3 and 2x4, and attached it to 24" long 1x6" sections. The key was just to make sure the height of the cross-pieces was at least 6", anything less and the bikes didn't want to stand up all that well.
- Tire width - they're all different, so check your bikes as you go, and adjust the spacing
- Sand the wood - you wouldn't want a splinter causing a flat
- Handlebar width - again, I put my bike in each successive slot before I set the next one to make sure the handlebars didn't overlap
- Use screws instead of nails - you might want to move some of the cross pieces to accommodate different tire widths or bike widths down the road
That's really it! Feel free to comment if you have any questions.