Which Circus Circus are you building? Which plans are you using? What are you using for wood? Do you plan to build the cowl from wood, or buy a glass cowl?

Do's
[ul][*] Make several spare copies of the plans before you get started.[*] Cut the parts "outside the lines". This will give you a little extra wood to adjust the fit.[*] Use a jig to build the hull. Starting out with a straight hull is critical for good performance.[*] Use good plywood. Avoid the typical home improvement store ply. Avoid "lite ply". Instead, buy airplane grade. The thin stuff that you will use for sheeting only comes in 3 ply, but get 5 ply for the other.[*] Use good hardware. [link=http://http:www.rossisales.com]Speedmaster [/link] is one good source.[*] Build it light. Cut lightening holes in bulkheads where possible. Make sure there are no areas that are completely sealed off (such as the fronts of the sponsons). Water may eventually get in there and you want some way to drain it out and the rest to evaporate.[*] Seal the inside of the hull with epoxy before gluing on the top decks. Use a little heat, such as a covering heat gun on low, or a hair drier, to thin the epoxy.[*] Make sharp edges on the insides and back of the sponsons.[*] Seal the outside of the hull with epoxy before beginning paint. You only need a thin coat or two. Make sure to smooth it BEFORE it cures and your paint prep will be much easier.[*] Install a 3rd channel needle valve. They make life so much easier.
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Don'ts
[ul][*] Don't slather on too much epoxy, it just adds weight.[*] Don't over engineer. Just as with planes, you need it to be strong, but the heavier it is, the harder it will be to get it to run right.
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That's a few to get you started.