There are six ways you could do this
1) Console Print so that when they type /buyadmin it prints a message in chat that tells them to check there console for instructions.
2) Print a message directly in the chat when they type /buyadmin
3) Get a MOTD plugin so that when they type /buyadmin it opens a MOTD with whatever you want to display in the MOTD
Advanced Motd 1.2 (updated)
4) Have a HUD message come up when they type /buyadmin
5) Get a advertisment plugin that displays message in your chat that you can alter that shows parts of the chat message in colors Also has a Auto respond feature so that it displays a message when they type /buyadmin in chat.
Autoresponder and Advertiser (with color and conditions!)
6) In-Game Advertisement System
- Display Ads on the walls of maps though this may be a bit over the top
In-Game Advertisement System
Im not an amxx plugin coder so please explain which one you would like and im sure somebody can help you
Also please make your thread Title specific as to what your are seeking do not use terms like WTF lool that does not tell us anything.