When you invite someone new to your company (Full Member invite) or to your project (Guest invite), you can choose if you would like that user to be able to upload files.
Full Member invites are people who are in your company, most users will need permission to upload files to all of your projects, but if you would like a user who is in your team to have a read only view of your files you can toggle the upload files permission off. This will apply to all the files on the projects you control, and any projects your company are invited to, even if the general file upload settings for your team on that project are set to on.
Guest invites are people who are in another company, but have access to your projects. You can choose if a company can upload files to your projects, and this can be different for each of your projects a company has access to.
Default settings and what to choose
Buildcloud defaults to file upload permissions ON for all users, as this is the best way to collaborate on Buildcloud, and you can always delete a file through the web app or web friendly view. If you are unsure what permissions to set, then leave them set to on and you can always revoke permissions at a later date.
I cant upload files?
If you are unable to upload files to a project yourself, then your company admin has removed your general permission to upload files, or the company controlling the project has removed permission for your company to upload files to that project. You can drop a message on the project newsfeed to ask for your permissions to be changed.