renault megane convertible not getting any compression?

Don't know who is doing the work for you but if there are no compressions on any cylinder then obviously there is a serious problem. You will need to go back and ask what was done when the head was off, was the head itself pressure tested,did it need skimmed,was the valve timing set up correctly when rebuilding,if all ok then I would guess the pistons would need to be removed for further investigations.

cdc
July 2015