We are planning to build a roof garden on a flat roof. The area of the roof is 25' x 25'. The concrete slab thickness is 6", and our structural engineer has provided sufficient reinforcements, as we had planned for this right from the beginning.
Before proceeding, we want to be doubly sure the roof will hold the weight, considering we will be adding a glass roof of approx. 7720 lbs (3500 kg)(including MS structure and glass weight). Add to this the weight of concrete planters, moist soil and plants (we have not calculated these), we are wondering whether a roof garden is a good idea at all…
Additional info – If we are going for a roof garden, a glass-roof for the garden is non-negotiable as we want to harvest rainwater and have invested in a large RWH sump underground.
Given the specifications, how much lbs /sqft can our roof hold? 
Best Answer
A structural engineer is required to go over your plan and to get the permit for the glass roof addition. Your roof was not designed to support the additional dead weight and wind load on the glass roof.