Profile with a namespace represents a database that user sees in the explorer. 

Namespace is mandatory if you want your user to have data in his database/profile.

If you already have a profile with the namespace to assign to a user, make sure to activate the checkbox in Designer column. Designer column allows write permissions over the entire database. If the checkbox in Designer column is not activated, that means the user only has read permissions in that database and is not able to create folders and models.