Can anyone explain scaffolding to me?

[SilverHawk]

We need to go over a polycarb roof and a flat roof to get to the tiles on the actual roof IYSWIM.
I'm hearing two different terms 'cantilever' and 'bridge', are they actually the same?
I'd also like minimum weight on the flat roof,so which is best and cheapest?

I don't know anything about scaffolding but if something is cantilevered, it is something supported at one end and sticking out.
So I'd assume a bridge would be supported at both ends.

Totally agree. That's why it's puzzling me because there's no other end to form a bridge.

if they can't build a leg at the other end, they might fix it to the wall of the house, or rest it on the roof. Sometimes they build a leg on the ground at the front of the house, and one at the back, and build a bridge between them, possibly also standing on the roof and windowsills.

Quite often they don't break any of the tiles when doing that, but you must have their commitment to replace any that get cracked or broken.