I have an addition on my house that has a rubber roof w/ railings and a door coming outside from a bedroom. It has a flat rubber roof which is probably 1/2-3/4 inch thick give or take. I would like to use this to put chairs and a table on. However, I know I would quickly ruin it if I punctured it with the chairs. I'm told it is ok to walk on but not to put anything on it. What can I do? Thanks