Hi Sarah,
It's a rewarding experience.
This search may help:
diy chameleon enclosure supplies UK
Might have been a better title for this thread too—to catch the eyes of UK members like
Pickle-cham,
Flick boy, but here we are.
One of the first decisions you'll need to make is whether you want to go bioactive or not, because it may effect your enclosure design & construction.
Next may be size. If you haven't already decided, I like this site for help figuring out enclosure size:
http://www.anapsid.org/enclsize.html
Then type of enclosure, which will depend partly on your local climate conditions & weather, and humidity levels to achieve & maintain for panthers.
The 2 main choices are screened or hybrid (solid sides, back, & door(s), screened top & panel beneath door(s)).
I can't emphasize enough using live plants only. Live plants help increase and maintain humidity.
If you use wood, I would stick to hardwoods (deciduous) and avoid softwoods (conifers). You can use conifers for framing, but try to get clear pieces rather than knotty—you're trying to avoid sap containing VOCs—and I would seal any wood with multiple coats of water-based polyurethane, both for that reason and to avoid dry-rot.
Other framing choices include aluminium, PVC, ABS, and probably one or two that escape me ATM.