CCTV lens size

[sjj84]

Looking at getting a IP camera to fit in my garage but unsure what lenses size to get. Ideally I'd like to mount it either centrally or in one rear corner being able to view both the roller doors. Mainly as I'm absolutely useless at remembering if I've shut the doors, the amount of times I've driven miles back just to check is ridiculous.

[sjj84]

5m x 5m approximately internally.