I built the XL version. It was fairly easy to fill in the gaps from the regular diy plans that are more robust, but my recommendation, as is the recommendation in the directions, is to take your own measurements as you move along as small adjustments are needed at times. Some of this was caused by me in having the big box stores pick my materials and have them ready curb side, so I ended up using some warped and bowed wood that ended up leaving things out of square. An obvious recommendation, but pick straight lumber. Also, go slow with the aluminum wrap and tape so it's as smooth as possible and check for "square" early and often. If you are going to use wheels put on at the first opportunity. Based on my errors I decided to not go the "disassemble" route and this is a permanent box now. It's not coming apart and it's is very, very heavy.
It is beautiful when done however. It is very hot and I am now looking for sauna pads and towels as the pool of sweat from a 15 minute sauna is legit.