I have two large flat rooflights (see images). Both have been leaking for about 6-12 months. I’ve been told that my options are to a) buy new custom made ones (the frame size of my existing skylights are 1110mm x 1710mm) or get rid of them altogether and board over. 
The only issue I have with custom made lights is that I’ve been quoted around £2400 for the pair plus labour on top. I don’t have that sort of money at the moment so I’m just looking for alternatives. Do you think change the glass would make a difference?

Any help would be much appreciated. 

Glass itself cannot leak unless it cracked/broken so replacing the glass is a non starter. You really need to establish where the leak is coming from which is not easy as water tends to track through the smallest crack/space. It could be the frame, the frame to roof upstand joint or the roof itself. Can you get up there and look for the smallest of holes or cracks to establish what can be done.

On roof with hose pipe