Fairly easy to make all you need is some sturdy solid materials, and something soft on top. I've made them in the past from PVC pipe, MDF blocks, and even cardboard triangles. This time I put more effort into them, something to be a more permanent solution.
Some 1x6s about 24-30"
Some 2x4s about 18-24"
Cotton cord (sash cord or cotton clothesline)
Couple of things to keep in mind, no nails or staples or screws or anything goes on top. Also, the 2x4s you will want on the short side, ideal length would be an inch less than the width of your project. If the 2x4 is too long it can be a trip hazard or at the least it will reach out and attack any powercords.
Nail your 1x6 to the 2x4 on the narrow edge, centered.
Knot one end of cord and staple to the end of said 2x4. Pull taught across the top and staple again and string back across to the knot, staple well on the ends.