building a 20 deg ramp?

[moturbopar]

Hi all I am looking at building a 20 deg ramp I can use to check my suspension mods and freinds mods. I have a couple question though. I am trying to find out what length the ramps need to be built to. I am also wondering about material to use. I am looking at bulding it out of some scrap wood 4x12 beam angle iron and square tubing I have. Do you guys think that 11" wide ramp would be enough if not how wide should it be?
Anyone here know what an averege 4" lifted blazers RTI is?
Thanks