I suggest the option for Confidential options within the data room folders, or specific documents.

For example, let's say you want to include all related documents in a data room for stage 1 discussions, but you don't want to give them access to some of the documents that are disclosed in stage 2. To keep the whole presentation organised you want all documents in one data room.

To create a separate data room for stage 2 is messy and confusing. I think a better solution is to allow a locked icon to be displayed for documents not accessible for that stage in the presentation.

For example:

Files in folders:

├── 5. Financial Models/
│ ├── 01MarketSize.xlsx
│ ├── 02RevenueProjections.xlsx
│ ├── 03PricingModels.pdf (locked icon)
│ ├── 04ProjectedP&L.xlsx (locked icon)

or

Folders:

├── 0. Executive Overview/
│ └── [...]
│
├── 1. IP Dossiers/ (locked icon)
│ └── [...]
│
├── 2. Property Listing/
│ └── [...]
│
├── 3. Development Pathway/ (locked icon)
│ └── [...]
│
├── 4. Marketing Strategy/
│ └── [...]
│
├── 5. Financial Models/ (locked icon)
│ └── [...]

You can then unlock them and allow them access whenever you wish, or by sending new invitation to inform them some docs have been unlocked.