Sorry about the lack of pictures, but by the time I decided this project to become and instructable I had already finished the base.

To made the base, cut four pieces out of the wooden slat, the dimensions are specified at the image, to avoid problems when assembling them I used a mitre and a clamp to keep the slat attached to it, this tool keeps the blade in a vertical position, avoiding irregular cuts, a minimal amount of sanding might be made afterwards.

When you've finished cutting the slat, make the definitive rectangle shape with it, play with the position of the slats to find the optimal configuration, once aligned, hold them together by applying pressure with the clamp to the short sides of the rectangle, now they're ready to be drilled. Mark the position of the screws, I've chosen to put them 1cm away from the edge. With some measurements, find the center of the slat and mark the position, once you have found it, drill the holes, which must be slightly narrower than the screw.

Once all the holes are drilled you can remove the clamp (or not if you prefer) and place the screws, I put some wood glue at each union to reinforce them.

TIP: If you remove the clamps when the holes have been already made, make some marking where two pieces come together (like circles, triangles, lines), if you disorder them, you can always put them together like a puzzle.

TIP: If your wood screws have an angled head you can use a special bit or a large metal bit (8mm for example) to make a countersink so the screws don't protrude.

To attach the cover, just draw the contour over some wooden board, cut it and attach it to the slat frame with more screws, I placed 2 at each side, leaving a gap between them of about 1/3 the length of that side. If you're like me, the chances are some of the slats or parts of the board will slightly protrude from the shape we're looking for, so grab that 80 grit sandpaper or an equivalent tool and start sanding until the edges are completely flat.

NOTE: It's not necessary to copy the dimensions to the millimeter, just get the general idea, and use the materials you find more convenient.

TIP: If you want your sanding to be more accurate put some sandpaper over a wood plank and use it to sand the wood, that will ensure your pieces will come out straight.