I would advise against this. It will be more costly and more dangerous in the long run. You will have computer equipment that are not in an enclosure, and if your protections fail against the elements then your investment goes down the drain.
You definitely have a point. However, the alternative is not building the rig (i live in an apartment with little space to spare). Not building is not an option.
I could find some alternative space somewhere in town perhaps, but it's an interesting challenge to build a rig that will run smoothly 24/7 and 365 days a year even though it runs outside. But sure... I may lose my investment if not done properly.
you do realize 24/7 and 365 days a year is impossible to achieve, there's always going to be some down time and I agree with other people I would advise against this kind of build simply because there's too many things that YOU have no control over and that could fail resulting in nothing less then the full loss of hardware, you have very little margin for error and if you think building a rig for outdoors is a feasible idea, I suggest you not get into mining until you have a better situation, not building the rig is a much better option than running the stupid risk of throwing hardware down the drain. its pretty much a no brainer on that one, btw unless you have lots of cash up front, good luck finding a location suitable for mining