RE: Customer portal many to one

We are in construction and work with several outside companies on a single deal. After banging our heads and speaking with ZOHO they cannot offer a solution. Can anyone here offer a solution?

USE CASE:  

Deal name = Big Deal 123

Portal users: Contractor, Architect, Builder, Inspector, Engineer

They all need to be able to access and submit questions and so forth on a single deal. Using the inbuilt "one to one" customer portal it works great but, only one portal user can see and work with a deal (one to one).

We need one like ZOHO Projects where an entire team can see and share files, notes and documents (many to one). Using ZOHO Projects could work because they understand many to one but, you cannot customize projects and add modules and fields that we need.

Can anyone offer something I am missing or a real solution.