I’m actually building jumps for the new barn I’m at (there are only two of us that ride so we’re splitting costs and getting help with the building).
I used 4x4s in 8’ lengths, cut in half, to make 4’ schooling standards. They are obviously lighter than 5’ or wing standards, and they are easier to carry around.
We also bought jump tracks with pinless cups, and used barrels (left behind by previous property owners, so free!) to make standards. Just screwed in the jump tracks and voila.
I’ve so far built one pair of brush boxes by cutting a skid in half (also free from the property) and adding feet so they stand upright (used scrap wood, also free).
If you buy 2’ x 6’ or 8’ boards (8 or 10 foot length) and cut a square out of the ends so that you have a hanger on each side, you have a plank.
Cut a 4’x8’ sheet of plywood in half lengthways so you have 2 pieces that are 2’ x 8’. Screw brackets onto the ends, or sandwich the plywood between two 1" x 3" boards, and you have a hanging panel.
I do also use the mini railway ties (I think they’re called landscape timbers in the US), especially for trot poles as they don’t roll if nudged. I don’t like how they sit in the jump cups, but I’m finding it very hard to get reasonably-priced round poles to use.
I’ve used PVC in the past and don’t like it at all. It’s way too light, horses learn to rub it, it rolls dangerously if knocked off, and they DO shatter in the cold (I’m in Ontario and they don’t do well at all in the winter). Would never use them as trot poles. I did pick up one pair of 10’ System 636 PVC poles which are much thicker than regular PVC, and are meant for all-weather use…but they were priced incorrectly and I got them for about $14 each. They should have been $40 each so no more of those for us.
I have 3 pairs of the PVC blocks and they’re great for cavaletti, but they’re not cheap. Light and weather-resistant though.
Oh - and I also have a few poles that appear to be cedar fence posts (not as thick as the actual fencing ones though). Got them from a friend secondhand so not sure where they came from, but our TSC sells cedar poles so could have been there. They are 8’ long and aren’t even thickness end-to-end but great for schooling.