Most shower glass I've seen includes a blue-green coloration that will filter alot of energy from sunlight - but if you de-rate the input specifacations and can accomodate the losses - go for it!
Some shower enclosure glass is tempered - some it not & not really sure how tell non-destructively... What may be most valuable is having the glass pre-installed stresslessly in a sturdy frame! Whatever enclosure you cap with the shower doors make sure the frame-glass have enough temperature heave-shrink allowances built in, and that the subframe won't rack or twist to leave glass supporting too much weight...
