Well, should do all the drilling and knocking first, before doing the plaster ceiling.
If not, all the dust will stick to the ceiling and it will be difficult to clean later.
This is inclusive of installing windows and grill, as all those will need drilling.
Water hose and wires for the air cond should be done at this time too.
And all additional/new electrical points.
Then only we start painting.


Sliding window usually does not have the ability to open fully, some of the windows can be opened while some will remain blocked.