Re:
Get doors, windows, walls and roof secured first. Bike locks won't be a problem if they can easily get inside the garage. Once inside and out of sight they can take as long as they like to pick/break locks on individual bikes and tool cabinets.
Brick or concrete construction with a proper solid roof and steel or uPVC doors and barred windows (if you must have windows) are a must along with CCTV. You can get decent motion sensing cameras for £50 or £60 that connect to the Internet and email you when something happens.