All steel products are susceptible to rusting when they come into contact with oxygen.
Rust can be preventing by painting over the steel or by hot dip galvanising.
Anti corrosive paint failing as anti rust paint solution
Hot Dipped Galvanising 
This is the process of immersing steel into molten zinc to coat it. Zinc bonds with the steel to form an anti-rusting and anti-corrosive coating. Hot dipped galvanised steel is used for many different functions including roofing, automotive parts and heating and cooling conduction systems. The coating has a lifetime of over 50 years in most weather conditions and requires hardly any maintenance.
Hot dip galvanising is the process we use on all of our sheds at no cost to the client. It is the best and longest-lasting way to protect your steel.

Paint Coating 
This method is more aesthetically appealing,
Many people consider this method more aesthetically appealing than the silver triangular pattern that zinc coating creates.
Coating paints work well in protecting from high temperatures and insulating the steel from fire. However paint coating has a 12-15 year lifetime and the steel is exposed to rust if the paint is scratched, chipped or dented.