It's usually best to purchase our universal kits that have the hardware pre-calculated. You get everything you need to build a trophy.
However, if you want to design your own trophy, and just want to buy parts, we have a document that will help. How to Build a trophy PDF

Keep in mind that if you are unsure of the rod length you might need for your column length, then it may be best to decide on the rod length first, then cut your columns to fit the space based on rod length.
It's easier to cut columns to specific lengths than to change the rods.