Calculate the number of posts you will need. The posts are what the floor of the ring will actually rest on. One post every 7' is sufficient for the dimensions of the wood used in this project. (See References 1 & 4) Kickboxing rings are sold in sizes approximately 20' by 20' to 25' by 25'. (See References 2) For a deck 21' by 21' this will require each beam to be supported by 4 posts. Four beams will be needed so that the spans do not run more than 7', therefore the total number of posts will be 16. Cut 16 one foot sections of 4"x4"
Nail each 2"x10" board to another so that you have twelve beams that are 7' long and 4"x10". Place the posts on the ground so that they form four straight lines 7' apart, with 7' between each post. Make sure that each line is parallel to the next. Nail the 4"x10" beams to these posts so that what results are four 4"x10" beams that are 21' long, each supported by four posts. (See References 1 & 4)
Nail the 2"x6" boards between each of the beams. The 2"x6" boards should be spaced every 18" apart, so that at the end there are 14 2"x6" spans that are 21' long, tying the four beams together. (See References 1 & 4)
Cut 1' off the end of each piece of plywood. Nail the plywood onto the 2"x6" spans. Using all fifteen pieces of plywood will leave a one foot wide gap on one side of the ring. Use the 1' plywood pieces cut off the larger sheets to fill this gap.
Nail one 4"x4"x4' post to each corner of the ring. Tie the ropes to them so that each side of the ring is fenced by three ropes, one above the other.