Elements

[Ashe]

Generating your element: The logic I would personally use is that you have to be able to find bits of your element in your surroundings (even specs in the air). Many element controlling fantasy characters do so, citing that "its too dry here for me to use my ice powers" or something. Take Magneto in the second X-Men movie as an example, he wasn't able to get out until someone came in with a ton of Iron in their blood stream. He didn't just shit metal, he took it from his surroundings.

I can see a lot of scenes where someone creates some Earth ability by pulling grains of sand from the wind blowing around them (and similarly ice/water abilities from drawing moisture). I also could see someone using Earth to create seismic abilities in the ground, so even if they are standing in a metal room, they can pulse seismic energy into the floor (this is my thinking though, I'm not giving a judge ruling on if its allowed). Keep in mind that Gaara himself carried around a massive gourd on his back at all times that was filled with (and made from) sand, in order to provide him the material that he would need to use his ability when outside of the desert.