You will need:
- IKEA "Slugger" casters $1.99 ( link )
- IKEA "Gorm" shelf $3 ( link )
- at least 8 small screws
- a screwdriver
My IKEA store didn't have the "Slugger" casters in stock so I had to get the more expensive "Rill" casters instead ( link ). Apparently they don't carry them in every store. They're $9.99 so it's coming out at under $13.
Step 1: Attach the Casters
Make sure there is enough room between the edge and the wheel so it can turn properly. I measured about an inch (2,5 cm).
The boards are about 0.6 inches (1,5 cm) thick, so don't use screws longer than that or they'll break through to the upper side.
Step 2: You're Done!
If you've got enough room left you can put a power brick or two in the spare space.
It looks surprisingly much like a skateboard when completed. BUT IT'S NOT. I'm about 220 (100 kg) and I almost broke it just because I had to try.