Armored Shelter is one of those Structure cards that can protect your creatures from attack, in a far more useful way than Defense cards can, though it still has its limitations so it won't be TOO powerful of a card.
One other thing I want to point out is those symbols on that top of the Armored Shelter in the picture. Those are magic runes, and I thought to put them there while drawing the picture for this card. The reason I put them there was to give the building protection against magical attacks in a way that would make sense in-game. In the picture, the runes wrap around the dome piece, so the entire word isn't shown, but it translates to "invulnerable". I think that was a good touch that I'm glad I managed to think up before finishing the whole card.