We did steel exterior doors.  Had them spray painted by body shop.  Still looks like new after 21 years.

Personally I do not like sliding doors.  The ones I have been around just have to much maintain.  The rollers.  Maybe there are high quality ones. 

Second reason is heat loss.  All that glass. Maybe poor seals.   Just turns me off.  

Could not give me a sliding door, but we are all different.  Enjoy.