How do you set the black backgrounds? I'd like making HD walls as well, but I suck as a mapmaker and would like to know the common approach
It is a seperate mesh using texture/black32.blp and the unshaded flag.
If you use milkshape (Which is unlikely if you're aiming for Reforged.):
To make them fit squares I just fit them perfectly in the default milkshape grid, and the scale them by 3.2 on each axis.
Generally, my walls is 3 by 1 in size (3 grid tiles tall, 1 grid tile wide.). If you want to make them fit together.
Feel free to pm me if you have other questions. More walls = more better