I used a heavy mesh similar to what many people use when making a grill out of a 55 gallon drum. I found it locally at a metal supply shop and they cut it to size for me (24"x24"). For this piece and a few feet of 1/8"x1" steel stock (which I used to run from corner to corner under the mesh for strength) I paid ~$20. I have this over my floor IB and I plan on covering it all with stained trim and acoustic cloth. Right now I can easily walk across it and I've even hopped up and down a little (but I only weigh about a buck fifty
). I'll have to load some pics when I get home.