Step 1: Materials
Half a broken longboard or other skateboard
Pieces of wood to hold up platform; they should be long enough to reach from the desired platform height to the mounting point you intend to attach them to at the other end, which is probably located near the rear wheel hub. I used very lame wood. You'll need to more wood scraps to make the two l-shaped brackets I'll describe later.
At least six wood screws.
Four bolts that fit the threaded points you're trying to attach the carrier to.
Four attachment points on the bike; chances are, your bike already has them. If not, you could improvise something out of hose clamps or zip ties.