I believe that the below pictures are worth more than 1000 words. Let me apologize for missing translation, so feel free to contact me via email if you need an explanation. The only two comment are that I suggest 15-18mm MDF board on the top (approximatley 3m2) and you will also need around 27 meters of metal profile 20x20.
Don't forget to adjust bar positions accordingly to the mounting place of your yoke and seats. My platform has been covered with gray carpet which is well corresponding to RAL 7011 cockpit base.