Creating .gii mask from .annot file

Hi there!

I am currently conducting a structural MRI analysis in SPM12 and I’m a bit stuck at the cortical thickness analysis. I would like to build a mask from the Desikan-Killiany atlas, which is implemented in the CAT12 toolbox, which I’m using. Since I am fairly new to brainimaging analysis, I am a bit lost on how to create a mask from an atlas in the .annot format.
I appreciate any inputs!

Best regards