Build your desk. Follow the instructions to build your desk. If you decide to buy a second hand desk and want to add casters onto the bottom that is a great option too. The caster allow you to move the table around to accommodate more kids around the LEGO table. It is also helpful for when little LEGO pieces fall and you need to retrieve them. The table we bought came with caster already on which was great. You can also not put casters on if you would prefer.
Measure where you want your baseplates to go on the pressed board. I had 4 inches remaining on the left and right sides and 2 inches on the top and bottom. Next glue them down with wood glue. Placing heavy books and/or holding them together with LEGO pieces is helpful. This makes them all look even, ensuring there aren't large spaces or bumpy areas. Allow to fully dry according to the wood glue instructions.
The reason 1/4 inch pressed board is the best for this LEGO table is that it is heavy enough to stay on the table but light enough that you can take it off if you ever want to use the table as just a normal table. Next you simply place the dry pressed board and LEGO base sheet on top of the built table.
And that's all folks! Simple, versatile, effective, and looks really cute!