A matrix is just a grid like a chessboard and looking straight down at it from above, the distance between each tile joint is ALWAYS the same.
For this reason, you can't actually get a vertical slope on a matrix.
But, you can get a 'wall-looking' effect by texturing the tiles around the edges of the matrix with a suitable texture and then raising the matrix's edge heights a fair bit. It's a quick fix and isn't great, but it doesn't look too bad if your character is inside the matrix.
I have a matrix tutorial for beginners on my web site which will point you in the right direction (link in sig at bottom of this post).
TDK_Man