My stepfather needed a deck at his duplex that wasn't permanent, and was relatively cheap.
I put this together in a couple of hours for about a hundred dollars.
Step 1: Design
Pretty basic, a square frame with 2x6s, this one is 8x8. We used 2x4s to cover it just because they were cheaper, but generally one would use 5/4 x 6s. Use something to space the boards evenly, I used the flat end of a carpenters pencil.