I'd say that the obvious choice for this scenario would be a GoPro. They can take pretty high resolution, wide FOV still images, they're pretty good with harsh environmental conditions, they have built-in time-lapse capability and they're not terribly expensive. They also have cases that allow you to hold the position of the camera even if it's removed.
The down side of a GoPro is that it has a very small battery, but it does allow you to input a standard mini USB power connector, so you can plug the one that's inside the building in to a wall, and you can get large USB batteries (like the units that charge cellphones externally), so you can swap them out very infrequently. This will be your weak point. If you can possibly get power to the remote units that will be key. Otherwise the cost of big USB batteries may be considerable. There are also photovoltaic options, but that gets very complex, and it doesn't seem that would be necessary in your case.
The maximum duration interval for the GoPro Hero 3 is 1 minute, and if you shoot at maximum quality you'll get 12 megapixel JPEGs that will be less than 5MB. if you get a 64GB microSD card you'll be able to fit over a week of footage on the card in a worst case scenario. If you use the 7 megapixel setting you're talking more like two weeks.
Obviously we're talking about a very large quantity of data in the end. That's something to consider.
Believe me, you're much more likely to get things right if you don't touch the cameras very often. You will need to set things up early and practice a little bit. Everyone I've ever known who has embarked on a first-time time-lapse project (including and especially myself) has done a few stupid things that have messed up segments of the footage. If you have things set up for a few days you can ingest that footage and see what you did wrong.