See this article that shows the default permissions for the Subcontractor role in Join; all of these permissions can be updated and customized as needed by an Administrator.
This role typically can create items, edit item information including costs, and has view-only access to most other information. By default, you can also limit whether cost editing should be restricted to their specific trade, in which case they will only be allowed to edit trade-specific costs. This same trade filtering can also be applied to other item details if you want to limit other functionality as well. They cannot change an item’s status nor see markups in items or milestones.