If your requestor knows what they want to review as part of their initial request, you can use 'deliverable types' as a way for them to add the name(s) of one or multiple deliverables.
From your 'project request definition', you can control if users can include deliverables to project requests.
From the last step of the project request submission process, the user will then see deliverables. They can click on the plus sign to see deliverable types.
Give the deliverable a name.
And for more than one type of the same deliverable, you can add multi-ope lines in the 'name field'.
Once saved, you can see the Deliverables all set to go.
And finally, the requestor can 'submit' and is done.