Breakable glass is easy, make a brush with the glass texture that you want then right click on the brush and select "Tie to entity" and choose func_breakable. Then in the func_breakable choose the properties that make your glass just like you want it.
A skybox is easy, make a brush covering all visible sky in your map and make sure that the tools/skybox texture is applied to all faces of the brush, DON'T nodraw the sides that aren't visible.
If you have HL2 there is an example of a 3D Skybox vmf file, if not there is this tutorial:
To make "Godzilla" people just place them in the 3D skybox. Without a custom model and a little coding this is the closest one can get to a giant.