I have a shop/garage about 100’ from my house that I would like to add to my alarm coverage. I do have wifi available out there. What are my options to extend my Ring alarm out there (door/window sensors)? I know there is an indoor extender, but my house is brick and I’d need to install it outside or does the extender communicate over wifi? Do I need another base unit? Can you have multiple base units working together?
These are great questions! 
The Outdoor Contact Sensor would be the best option here.
For your indoor Alarm devices, we advise keeping those in your immediate home or house structure, as they are not intended for outdoor use (unless otherwise stated). Additionally, Only one Base Station can be used per location, which is why it is recommended to keep your Alarm devices within a reachable distance to your centrally located Base Station.
Check out our Help Center article for setup and using the Outdoor Contact Sensor, for more info.