Code:
 on *:join:#: {
if ($nick == techchef) { 
var %random $rand(1,N)
if (%random == 1) { msg # Welcome my creator!}
elseif (%random == 2) { msg # Welcome Master }
elseif (%random == 3) { msg # pizza }
etc.....
elseif (%random == N) { msg # Message }
}
}

Replace the N with the amount of phrases you want. After the first if statement then do elseif.

Here is my multi channel bot smile https://github.com/zapdos26/mIRC-Twitchbot-Windows