Recently while trying to realize a character concept (basically a fantasy Iron Man without flight nor energy blasts), I've found out that there was no Armor magical ability that let you don and doff quickly by yourself without penalties. If such ability existed, how much worth would it be to add to a full plate armor? Or better yet, does such ability already exist?
p.s. I was struggling on where to post this, here or one of either Advice or Homebrew, but gave up and decided to post this here.
Advice would probably be best
While there's no armor ability for it, you could probably work one out with your DM based on the Swift Girding spell
In addition there's this armor
edit: ninja'd! Was working out some math that just became unnecessary but oh well!
In #30 Portable Rooms, one of the rooms is an armoury that lets you don/doff an armour of your choice instantly.
Also, there is the spell instant armor.
For other options, you could re-skin the gravity suit or smart armor from the Technology Guide or use the rules for Building and Modifying Constructs from Ultimate Magic for the construct armor modification (clockwork soldier is probably one of the most cost-effective options other than armor as an animated object).
Knights of the Inner Sea has Serren's Swift Girding (Magus 1, Paladin 1, Sorc/Wiz 1) that will allow you to clad one person per level in their armor. The spell takes one standard action.
The same splatbook also has a magical item, Armiger's Panoply, that will allow you to use a command word to become armored or even swap with the armor currently in the item.