I dont know about iron but steel wood work best. but its a lot more practical and easier to make one out of pvc. you just need a couple of 2x4s, a small sheet of plywood, and 2, 2 inch pvc pipes.
If you want to know, this is how you make a pvc rail.
1: cut three peaces of 2x4 to be how tall you want the rail to be, 2 to 3 feet long should be good. space these out evenly, three legs will work until the rail is about 8 feet long, once you get to around 10 feet your gona want to add more supports.
2: Cut another 3 2x4s that are 3 feet long, this is what touches the ground. your going to want to screw these boards togethor to make a "T" shape.
3: Cut another 6 2x4s with 2, 45 degree angles on each end to make the "T" into a triangle.
4: take an 8 foot long 2x4 and screw the legs to this, put the screw in from the top of the 8 foot 2x4 down into the vertical part of the legs(the legs are the "T"s) the legs on the outside should be about 6 inches away from the end of the board and the third leg should be right in the middle.
5: After you screw the "T"s to the 2x4 cut 4 right triangles and 2 equilateral triangles out of the plywood. Also cut out three trapezoids to support the connection between the diagonal and vertical boards on your legs. screw the right triangles to the outside legs, the equilateral triangle in the middle and the trapezoid on the intersection between the three boards on the legs. Reference what your doing to the picture... by now your rail should look like this (minus the pvc):
6: take 8 feet of 2 inch pvc and put it on either side of the 2x4 and screw it in so the screw goes through the 2x4 then into the pvc. repeat this on the other half of the 2x4. space the screws out about every foot.
7: if you want even more support you can add a board like this:
Thats how you make a rail
