From SteamFriends Wiki

By default AMX radio style menus (like Mani uses) are not working in HL2 based mods. However, it is possible to make this work. The code is being used, the menu resource files are just not making use of it correctly. There are a few lines that need to be added in to make the menus show up, the issue in a base mod is that the text and background are basicly not defined so it just is blank. This is the code that needs a fix in HudLayout.res (this has to be extracted from the gcf):

HudMenu{"fieldName" "HudMenu""visible" "1""enabled" "1""wide" "640""tall" "480""zpos" "1""TextFont""Default""ItemFont""Default""ItemFontPulsing""Default"}HudRadio{"fieldName""HudRadio""TextFont""Default""visible""1""xpos""10""ypos""c""wide""Default""tall""Default""text_ygap""2""TextColor""255 255 255 192""PaintBackgroundType""0"}

Example of ingame radio menu:

Also make sure you bind keys 8, 9 and 0 to the right ones so BACK and EXIT functions of the admin menu’s work.
bind “9” “slot9” etc

Thanks to Yahoo, developer of SourceForts for this great example.