asterisk users - Mar 2005 - Ideas on how to make a script for using random zap channels

Hey Guys.

Im trying to make a script but I need some ideas on the logic behind it.
Here is what Im trying to do:

I have 2 zap channels. I want to make a macro that would do some random
choices on which of the 2 zaps to use, then test if it is available, if it
is, make the call, if not, then go to the second one and test it too, if
available, make the call, if not, then playback the all ciurcuits busy
prompt.

I now I have to use random, goto, chanisavail but any logic ideas on this to
make a clean macro?

Thx Guys