I ran a lot of conduit in building steel back in an earlier life. An extension ladder is fine, but a pain to move from place to place, and about useless if anything has to be done between the trusses. You can drag a step ladder along as you run the conduit. We used to use roll around crank up, hydralic, or air lifts [outlawed] back before the self propelled scissor lifts became availible. If you want something very safe and want to get the job done quickly, rent yourself a four wheel gas/diesel/or electric JLG boom lift. [JLG is actually a brand name, but that is what we called them.] Remember, money may be important....but the ground is hard...and it gets harder as you grow older... If I remember correctly, JLG stands for John Lewis Grove, one of the Grove brothers, that broke off from the Grove company that makes Grove mobile cranes...and went into the boom man-lift business..... NICE units..!!!