Step 1: Materials needed
A 12x12cm brass, copper or tinned metal plate, a BNC chassis connector, a BNC cable connector, 35mm thick PE or styrofoam (can also be thicker) and some 1.5mm2 single core wire. This stuff is used in the netherlands in 220V in house cabling.
Other possible materials:
I can imagine that people want to use other materials, like a pipe to mount the antenna wire on. If you could get a pipe with roughly a 35mm diameter, you can use that IF the material is good for radiowaves. There is a very simple way to find out. Place a piece of styrofoam in your microwave, together with a piece of the material you want to use. Turn on the microwave for 30 seconds. Stop the microwave immedeately if you see the other material melt. Now check out how warm the other material is, if it's not warmer, or a little warmer than the styrofoam, you have found suitable material, if it has melted or is very hot,that you're dealing with lossy material which absorbes microwave radiation and turns it into heat, this material is useless for making high performance antenna's. This trick works so well because the WIFI band is at 2.45GHz and microwaves also radiate at that frequency, so it's a perfect test. Some very good materials are PE tubes, teflon tubes (if you can afford them) and PolyProlylene tubes.