Roof for a bridge crane

I don't think it really matters all the ones if have seen when working on cranes have been a simple gable designed just to keep rain off the machinery. Best way is to look at the budget and build the most practical (to simplify maintenance) within the budget. A good practical roof is better than a pretty roof that restricts access and you keep banging your head on doing maintenance

#1 Form Follows Function

If it is inside, perhaps you need no roof at all.

thanks for the information. Kyoto, the roof is necessary . Another question, what kind of steel? A 36?

Unless the roof needs to support something other than itself, Any water resistant material will function well. Try to slope it so water collected does not drain in a way that will interfere with the operator. Further conceder draining the runoff away from sensitive components of the crane. Aluminum, mild steel or fiberglass would seem like good choices.