grupoferromax.com, with branches in several locations in Nic.
I was in town today with some time to kill and happened to be at ferromax when they were firing up their machine to make roofing out of a roll of sheet steel ( they can cut it to your length to the nearest centimeter.).
They seem to be the source of the upgraded construction materials I occasionally see in the area. They have things like galvanized perlins, several types of metal roofs, including some that are aluminized instead of galvanized (they claim they are cooler and last longer). They also have the new rebar that is made of steel and it is stronger that iron rebar on a size by size basis. I had heard of this rebar but was a little skeptical. Their rebar has a distinctive screw-like pattern on it and it is clearly stamped Ferromax so you should be able to ID it on the job site.
I haven`t bought from them, but will check them out the next time I have a project. the galvanized materials make sense as they will not have to be painted and will last longer.