Temperature issues and methods of avoiding attic heat came up in this thread a few weeks ago: http://discussions.flightaware.com/ads-b-flight-tracking-f21/temperature-limitations-on-the-equipment-t26939.html
I’d recommend reading the entire thread. 
Toward the bottom of the thread, I posted a pic of one of the setups I run and provided details of how I keep it cool. User ‘beckerm13’ also posted a pic of his setup, which has only the antenna in the heat and leaves the Pi and SDR dongle just on the other side of the ceiling in the air conditioning.
Unless you’re just hardcore about wanting to move it outside, I’d leave the antenna on the roof, install an inexpensive amp near the base of the antenna (just inside the attic if you don’t want to have to worry about waterproofing issues), and run as short of a piece of coax as you can get away with to the inside of a closet ceiling and mount the Pi there.
Even though this is a cool project, I think you’re going to go through more trouble and expense than it’s worth to install the Pi outdoors. If the length of the feed line from the rooftop antenna to the outside enclosure would end up being close to the same length of running the feed line down through the attic to the ceiling of a closet, it would be worthwhile to just do it that way to save the money on the enclosure setup and keep your Pi in the air conditioning. A couple of extra feet on the feed line from the antenna isn’t going to make a noticeable difference - and really won’t matter if you add an inexpensive amp.
Matt
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