[Stiglr]

That's a VERY general request...

What kind of bridge do you want? A simple stone bridge over a brook? A rickety rope and wood bridge? Or a modern city bridge spanning a Bay or River?

That has a lot to do with how much detail is in it...and you have to determine how much detail you want it to have.

Also, what are your data sources? Do you have blueprints of the bridge? Detailed photos of its structure?

Depending on the answers to those questions, this could be a 10 minute job or one taking many many hours. Also, if it's a modern steel bridge with many wires, sections and whatnot, there are some automated features that can cut down the amount of time you spend creating the entire span.