If you're an Org Admin you can give other users permission to create model stacks.
Click Setup, then choose Configure User Role Settings.
With the Organization tab selected, scroll down to Model Explore where you’ll see two options:
Access Models – this controls whether users with a given role can access the Models module menu and Model Explore ( +).
Create Model Stack – this controls whether users with a given role can create a new model stack in a project. Users with Grant become the Administrator of all the model stacks they create and model stacks created within their organization.