Do you carry outdoor rubber rolls? If so what is the largest you carry I would need (1) 21'x 21' ?

All of our rubber rolls can be used outdoors. For the size you are looking for, we would suggest our 8mm Strong Rubber Rolls. Here you can cut the rolls to your desired length. The rolls are 4' wide so you will need 5 rolls to cover area 21' long or you can go with 4 rolls which will be a little less than your area at 21' long.