I want to create a list of documents that allow the user to group like documents together, but can't seem to wrap my head around how this would be done.

Invoice 1
Invoice 2
Invoice 3
Drawing 1
Drawing 2
Drawing 3

Invoices
->Invoice 1
->Invoice 2
->Invoice 3
Drawings
->Drawing 1
->Drawing 2
->Drawing 3

My thinking was to design a table as follows

ID Parent Document
1 2 Invoice 1
2 0 Invoices
3 0 Drawings
4 3 Drawing 1

But as you can see the problem I develop that the top level items will not sort correctly with the Parent as all the top level items would have a 0.

When designing a document indexing system for my employers (in a previous life ) my approach was to create a hierarchy of:

>Contract number and details
>>Accounts
>>> invoices
>>> quotes
>>Drawings
>>> CAD memos and instructions

>>Documents
>>> To Client
>>> From Client

Each level was given access rights commensurate with their position or requirements.

CAD couldn't access Accounts or Documents
Accounts couldn't access CAD
Secretaries/PAs could only access Documents and CAD memos.

and so on ...

At this point, I am not really concerned about access more about managing the list like a BOM in the sense that the top level item can have subcomponents until you get to the bottom lever. An example would be as follows:

Computer
>>Monitor
>>>glass
>>>frame
>>Tower
>>>power supply
>>>tower Box
>>Key Board
>>>101 keys
>>Mouse
>>>wheel
>>>ball

This would allow me to group related documents together as documents are realized. At first, I may only have a single quote but later I may have several quotes that I would like to Group together under a common header called Quotes.

Ok so you are looking at creating a "picking list" system rather than a document index system.

I guess, I am not sure what a picking list is, if you mean a Bill Of Materials (BOM) than I am looking to create something more of a picking list for documents.

A picking list is what would be created for an assembly process to have the materials collected from stock/inventory control.

For a collection of documents would be a portfolio, So is it that you are wanting to assemble a portfolio for the documentation of a particular computer assembly?

Yes, that would be correct. I would like to create an assembly for a porfolio of documentation.