Im a welder fabricator and use a 355mm cold saw to cut box angle and tube, these are expensive for most locost builders at about £2000 but you can sometimes pick one up of the bay for about £500 and the blades are about £50 each, resharpening is £10 from saw point, we also have a 12" band saw which is hardwork to set up for angles, id suggest getting a rage 2 355mm,
http://www.evolutionpowertools.co.uk...ion_rage2.html we use one when doing site work and are very powerful, you can even get blades that can be resharpened.