Please help, Im trying to install CAESAR IV and I got until the end and it says "REQUESTING INSTALLER"?
I click on offline installer and says GOG GAME SETUP

You will need to be a lot clearer on what you have done, what has gone wrong. The above does not really help.
All I can recommend d is to download the offline installers from the website, and run those and install to a non windows directory like c:/mygames

If you're using Galaxy, I can't help you.
But why not simply use the offline installers?

1) Hover over your account name
2) click on "games"
3 ) enter "Caesar 4" in the search mask
4) click on the "offline backuo game installers" ---> click on the file(s)
(I only have Caesar 3, so I don't know if Caesar 4 comes as a single file or one (.exe) and one or more (.bin) files)

5) after downloading, click on the .exe file to install the game.

The installer will ask you, whether you want to change the installation path...do so, if you wish.

After the installation is done, you can start the game immediately by clicking on [start] in the installer's window, or later by clicking on the desktop icon of Caesar 4.