roof? glass? i’ve seen that alot. if it is, they have built in gutters on interior side (bottom of top) they may be clogged up. also on outside (top) they would use a rubber gasket, it probably shrank and has one -two inch gaps now. my experience in replacing glass shows that removing glass gives access to those gutters clean them out clean glass and gaskets and replace. seal up the gaps only, too many people use too much sealant and may clogg the weeps (drain holes). it easy, little tricky getting at all the glass. planks will be needed. they are made to let water in, into the gutters and drain out at bottom of roof. hope that helps