To restrict access to specific folders for contractors, suppliers, or clients, navigate to the Folder under the Lead or Job for which you want access to be restricted.

On the right-hand side, next to the folder, click on the ⋮ button and select Sharing. This will bring up options for sharing and access for clients, suppliers, or contractors.

Selecting these will allow the contractor, supplier, or client to see the subfolders and files within the folders, provided they have access to the job.