Don't know if you just wanna build one or if the Prowler is too pricey, but if you have a Dicks' sporting goods where you are they actually carry a line of sleds that are built just like prowlers. I got one for under $200.00 and it's pretty damn durable.
1) I heat treated mine, and the parking lot is soft. They wear the parking lot. Your milleage may vary. Make sure you plan for replacement regardless. Very little steel, and a couple bolts now will save you alot of grinding later.
2) It weighs what it weighs. Unless your planning to have some sort of formal competition, it shouldn't matter.
3) If by worthless, you mean difficult and worthwhile than yes.