This is how

x 35mm screws. Repeat the process to build the other long side.

Do exactly the same for the two short sides, but use five short lengths of the lap log boards for each side.

Take the 38mm x 38mm beam and cut two 94cm lengths. Measure on the inside of each side 40mm from the bottom edge and draw a line across the width of the side. Then glue and screw one of these pieces onto the line using the 60mm screws. Use at least four screws on each side, as the base of your plant box will rest on these beams.