I would just start with some poles on the ground, little 2x4s should work. My three year old, Ruger, was a dipstick aout his feet so we did a lot of trotting over those. Depending on your horses stride, you should space them about two steps apart. (You'll have to adjust probably, Ruger's stride is two BIG steps for me but Selena's is only about one and a half big steps...xD)
Also, if you want to raise them, you could use some feed buckets or lay barrels down and make some small crossrails to trot over. I wouldn't lope though because it's really hard to get a horse's stride right.
You could always lunge him over too. :) Good luck!