When I am giving like thickness to the glasses with extrude and then alt+s it leaves the inside empty or void, then if I press shift+n it's still the same, I dont have backface culling on but if I activate it now all my model goes to ..., what can i do?
It sounds like you just need to add faces at the original place.
Or this: https://blender.stackexchange.com/questions/43505/how-to-extrude-and-leave-the-original-in-place
If that's not the problem, maybe sample images?
That may happen because the edge of your glass is connected to something.
In a situation like this:
you wouldn't want it otherwise.
It could be that you can't see that the edge is connected, but it probably is. (For instance when you have your edge (not yet filled), E, Escape, Grid Fill, E....)
