2. 6' 1x12
4. 3' 1x10
4. 9" 2x4
1. 6'x3' piece of 3/8 plywood
a box of 1 1/2" interior wood screws.
First attach two 2x4s to one of the 1x10s (one per end lol) like a little table, and remember to drill pilot holes to stop splits. Make sure the ends are flush. They both need to mate with the 1x12. Now make another.
Next make a box by screwing into the 2x4s. Once again flush ends people, and 1x12 always need atleast three screws per joint.
Now measure n mark every 2ft down both1x12s. This is where your "shelves" go to support the matress. Once again pilot holes then screws.
Finally putty, sand, n stain or paint.
ps don't forget to round the corners on the 1x12s