indoor roof light fuse, where?? Cutlass '80

I simply cannot find the indoor roof light fuse from the fuse panel,
where is it??

Look for the fuse cavity marked "CTSY". Usually a 20 amp fuse, and if it's blown it should get your lighter going also. CTSY is short for courtesy lamps.

I think it must be somewhere else than regular fuse panel. I checked all the fuses there and no-one has effect on roof light :(

If you are checking the fuses visually only, you can get stung. For a circuit to be complete, you have to see battery voltage on BOTH sides of the fuse. If your voltage is absent on the battery side of the fuse, then you have power distribution problems. If it is absent on the load side, you either have a blown fuse due to a short in the load circuit, or you have a faulty fuse. Fuses can look intact and still not work.
I am 100% sure that the CTSY fuse is in the main panel, which is actually the only panel. If I'm wrong, I'll buy you a tank of gas.

Nice offer! :)
I have used light pen to check fuses.
And when I'm pushing the door switch which controls roof light, I see no changes on the fuse box.

I want to find fuse which has voltage when roof light is on.

The CTSY fuse that controls the light you speak of is an always hot battery side supply fuse. IOW, it won't show voltage when the doors open because it supplies voltage to one side of the lamps all the time. The door switches supply the ground thus completing the dircuit so the lamps light up.

heres a curious question?? did you check the bulb? or if the door triggers have corrosion around them?