So the door shields aren't allowed
 

Why are the door shield aren't allowed in-game?

They represent ingame tiles

As already stated, you cannot upload shields that act as in-game tiles, even those that are not identical to the ones used in the tileset.

This has already been discussed in the thread below:
https://www.graalians.com/forums/showthread.php?t=40291
There is also a full uploading guide there.

This sums it up well. If you have other questions about the uploading rules, you can click here (or on the link Mashboyellis posted) to visit the thread dedicated to such things. To keep discussion about uploading rules in one place, I'll be closing this thread.