custom wizard help

we need to develop a custom wizard which will allow the users to

first, select a class,

second, selects items only in that class

so it is more like a two-step wizard selection in production hierarchy.

I understand that this has to be done by custom wizard, but i do not know how to do it.

Can anyone give me a sudo code please, lilke which RPAS object i should use?

Thanks,

Steve