Creating an interactive form for clients

I'm trying to create an interactive form for my clients. The part that I am having trouble with is that I have list of services that are available to the client (20 - 30) and each of these particular services have a number of deliverables that the client may or may not want (anywhere from 2 - 40 deliverables per service). I would like to allow the client to choose the specific services they want by checking a checkbox next to that service and then, based on the checkboxes selected, have a list of deliverables populate that will allow them to select the deliverables that they desire (one again through checkbox selection).
 
This probably is not that difficult to do, but I am entirely new to this and really don't have a clue where to start. Any help would be greatly appreciated.