I also had a hard time finding large thick branches for the structure and they're ridiculously expensive to buy. Ended up using these that I found on Amazon. Still not cheap but it was the cheapest option I found:

https://smile.amazon.com/gp/product/B084Q9T4P1/ref=ppx_yo_dt_b_asin_title_o07_s00?ie=UTF8&psc=1

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I haven't got a tutorial but I do have the dragon ledges on my cage and they're fairly simple. It's just two lengths of wood about 1/2 inch thick with some spacers between them then screwed into the frame. That's all. I feel like you'd be able to replicate them pretty well by just looking at some closeup pictures of them installed. I can take some of mine from different angles if you think that would help you out.

My setup is the dragon ledges with the branches I linked from Amazon as support as the base. I have several plants in it and the thing is super sturdy. There are pics if you check my post history (plants are a lot bigger now and it's still sturdy as a rock)

I am definitely not an expert but this setup has worked well for me. I have a male cham and he explores all over every part of it.