Foot bridge design

I would like to have a fairly broad foot bridge over a small stream in the center of our property. It should be tasteful but also practical as it will be a significant feature. We are here northern Uganda. Does anyone know of a website that gives ideas of how to design and build such bridges.

Also how durable would I expect untreated Mahogany to be is I used it to build the bridge with it. We get plenty of rain in season. I cant think of any other timber that might be durable and yet is available here. I could combine it with metallic tubing for the verticals perhaps.

Thanks