With no sides on your attic you can use one of these: FANTECH RE-6 N/A RE Exhaust Fan Fans: Compare Prices, View Price History and Read Reviews at NexTag

If you don't know much about construction you should have someone that does install it. There are certain principles at play as far as weatherproofing and I'd hate to see you fuck up your house.

I grew in (what turned out to be a shittily constructed attic) many many years ago and could see the light through cracks that went 360degrees around the house. lol. and that was before it was all legal. Don't sweat the choppas.