I would personally stay away from plexiglass...I've found it tends to crack to often, even the thick stuff...just wouldn't take the chance! It'll be more expensive but I'd use Lexan...it's unbreakable. You should be able to use a lot thinner sheet vs. plexi vs. more than double the strength. Check with your local glass/plastics supplier...they should be able to tell you what thickness you would need to carry X amount of weight. Also we had an effect similar back @ the old Brigantine Castle in the 80's (man that makes me sound old!) but these plastics tend to scuff/scratch easily....so if your going to have an actor on it either put him in socks or some kind of soft slipper/boot, otherwise your not going to end up seeing the actor by the seasons end thru the scuffs & swirls! Lexan does make a "scratch resistant" type but it is EXTREMELY expensive! Just my two cents!