Alternatively, don't use panels at all and only work with a 2dimensional array (f.i. 0 is no tile, a positive value is a solid block, a negative value is a walkable) and then use draw_quad to draw appropriate bitmaps. Example:

BMAP* bmap_tile[7];
#define SIZE_X 13
#define SIZE_Y 20
var field[SIZE_X][SIZE_Y];
var tile_size = 32;
...
for(i = 0; i < SIZE_X; i++)
{
for(j = 0; j < SIZE_Y; j++)
{
if(field[i][j] > 0) draw_quad(bmap_tile[field[i][j]-1],vector(i*tile_size,j*tile_size,0),NULL,NULL,NULL,NULL,100,0);
}
}

The bitmap array "bmap_tile" contains your tile images. You can easily perform collision detection by checking the "field" array, when your player at position i,j, check field[i+1][j] to see if you can go right etc.