First I wanted to thank you for a very solid project. This is exactly what I needed as a good simple base for my personal project.
I added a bit of code to the Copy Files script (Actualy one line) to make it easier to open the folder if it has not been created yet.
Should be the new section for OpenCustomFolder as this version will create the folder if it does not exist.
The same should be done in other locations such as in Add Drivers
Theres also no check in Make Iso script for if the directory given is the root of the drive, from what i see its possible for the script to run properly and create an unbootable flashdrive (As the wim would be in the wrong place example: f:\hahaibrokeit\sources\boot.wim) a quick check for the length of the string should be enough because all valid drives should be 3 or fewer letters.