I have built both the 4" and 8", I liked the four so much that I wanted the bigger one, they are super sturdy, birch plywood and braced for a tornado, you will need a set of clamps of different sizes. Don't believe that you can glue them with masking tape as they claim. On the 8 " I bought Decwares DSR 8
modified fostex, it cost around $100.00 extra but it is well worth it.
I am running the 8" with the sex and that is super sweet, I gave the 4 " to my daughter and she loves them, I would go all the way for the 8" if I were to give advice, you will not be sorry.
I have enclosed some pics for you to see