I have hunted many years in the Southeast areas of Ohio. Much of that hunting was done from deer stands - mobile (mass manufactured produced steel) stands as well as the old fashioned home-made stands. Dad has about 15+ stands on his property. At least half are home made deer stands. My tip here is to easily provide to you a very sturdy and long lasting wooden deer stand base.
I have seen deer stand bases made from several different products - i.e. shipping crates, several 2X4's lined side by side, etc....
The best deer stand base by far that I have hunted on is using the following materials:
Simply take the 4X8 sheet of plywood and cut it in half on the long side so you end up with two 4X4 sheets of plywood. Place one sheet on top of the other and screw together to create a one 1" thick 4X4 (screw all four corners plus up each side and also straight line on front top portion of the wood). Do not screw together bottom/back portion of stand base yet. All screws should be from top of board towards bottom.
Then take your 10' (or 12') treated lumber and cut in half. Place it flat side down on the underside of the 4X4 so that the center of the wood is on the 18" mark inside of each side. Even the end of this cut 2X4 so that it is even with the back of the platform and sticks out the bottom front of the platform. Screw these from above (stand side) into the platform using the 3" galvanized screws (use at least 4 screws per supporting board).
On the back of the platform in between the two supporting boards cut out a small curve within the 4X4 using a jig saw or other tool to allow the back of the platform to rest correctly on the curvature of a tree. Using the 1" screws then connect the back side of the platform around this cut curvature.
The supporting boards will stick out from underneath the platform by 1' or 2' based on the size of stud purchased. You can connect your ladder preference to these for a completed deer stand.
Add some astro-turf or other outdoor mat to the floor of the deer stand platform to eliminate noise while standing or sitting.
Recommendation - use 2 - 2X4 wolmanized studs to connect each side of your ladder to the tree (in addition to any straps). I use a U-Bolt and drill a hole in the wood to connect the ladder to the stud and then bolt the other stud sides together on the other side of the tree. (You can screw or nail into the tree directly only if this is acceptable within your state's regulations).
There you have it - a deer stand platform that will last many years.