4 years ago:
cs:go minimaps are in the .dds format.
This is the plugin I used to save my one, so if your using photoshop here is the link:
The files have to be located in csgo/resource/overviews/.
So basically you follow that tutorial up to the point where you create the vtf and stuff, but instead you make a .dds file.
You need two files in your overviews folder for each map.
The txt should contain the regular stuff :P
Files Pakrat fine. The txt file will be picked up automatically, the _radar.dds file will have to be added yourself. (make sure you dont leave your whole computers url in)
"material" "overviews/de_examplemap" //no _radar on the end this time.
If server owners want to use maps that don't have pakrat'ed minimaps, then check out this plugin.
[CS:GO] Radar and loading screen downloader
Ok, hopefully I wrote it down all correctly :P I did get it working myself.
EDIT: Forgot the plugin link, and updated the post in general.