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.