How have you attached the glass lid to the cement wall around it ?
I have screwed a 3"x2" timber wallplate to the top of the back wall. The lids are fixed with 'tee' hinges and I have used old casement stays to adjust the ventilation opening.
I'm guessing you have a couple of cold frames around the garden and you move the plants around based on what stage of growth they are at.
As it happens I have but in that one in the picture/s I have made an adjustable floor!
It is basically a duckboard sitting on bricks.
When the plants are first placed in the frame the floor is set to its highest position.
As the plants grow in height the floor is lowered (to cater for the plant height) by removing sucessive layers of bricks.