This is one subject that my wife gives me lots of poking about! I have 11 towers of my own and have built lots for others. and i have two new ones to try and finish this weekend.
My son and I just love building these things and it seems with every new they get more elaborate.
I have metal and wood ones and thinking of building one that uses a metal base and a wood shooting box.
I try and use treated wood for the floor but i have used free untreated plywood for flooring. actually i have one I am putting up this weekend that has 3/4 OSB for flooring. Now i don't ever leave a floor untreated . You can buy mistint paint at lowes or home depot for around $5 a gallon and give that floor a good coat of it.
That helps keep the weather from getting to it.
Also the sides i usually use 7/16 OSB and paint it also.
always paint the stand!even metal!
Now if your going to build wood you must figure out how you are going to put it up. I have built them on site and really thats the easiest. if you build them at home you are going to have to have a way to get them there and up. they get real heavy real fast!
I use a tractor with a front end loader. it is a must for mine. For example the one i will be putting out this weekend is a 4x6 box it got to bulky and heavy for folks to pick up. The base is a shorty at 6' tall but bulky and a little heavy. so i built it modular. the roof is 2x4 frame that carrage bolts to the box by using the structure 2x4's. I always seal any holes in the roofs tin or shingles prior to installation.
The box is carriage bolted to the base by four 1/2 bolts . the under structure of the box is beefed up for support and just drill the holes for the bolts.
ALWAYS use quickcrete to anchor these things! even if you think it's stable use it!
But anyway you need to think about how your going to set it up! If you have a generator and can get a truck or tractor with trailer where you are working it is ok to spread it out over a few weekends to build. I have used my atv with a small trailer to haul in materials.
Timbercruiser gave some good advise on the carpet. i pull all my carpet at the end of season and store them in a building to keep them from holding moisture against the floor. Now i have started putting flaps on mine using small hinges. I cut a peice of OSB to cover my openings and hinge them up. I run a piece of string over the upper base to be able to pull them open when i want . you can put some nails to tie it off to inside. build a stop for them to keep them from flapping in wind .
thios helps keep rain out and leaves and such.
Anyway plan well before you build ,use your imagination and have fun.
There is just something about sitting in a stand you built on a cold rainy day with your mr heater all warm and dry when those that only climb trees are sitting at home watching OLC!