Progress (or lack of) so far then :-
Loop parts of roof anti-lift system will be screwed to the corner uprights of the fixed observatory framework.
I shall keep the storm lock-down latches and window bolts so won't need the linear actuator to bolt the roof closed.
Limit switches are well on the way to being sorted out.
Rain detector will be tested when we get some rain.
Spring to tension chain and limit force used to close roof, works well.
Push buttons on the control unit will provide local control - Open, Close, Abort.
May use coloured LEDs on front of control unit to indicate status - Open, Closed, Closed after rain detected, Fault, etc.
I plan to include RPi in the control unit box for remote control and feedback.
The bungee cord for pulling the window open seems to be loosing strength so I'm going for another solution with lever and spring.
The small chain pulley needs a thicker screw into the baseboard - current one is bending from the tension in the chain.