sadly I have no garage and winter is coming! What is the best cover I can buy for my 911

 

Drve it!

 

I got an all weather one off ebay brand new for $50. It's very durable.

 

Best one imo is the factory Porsche outdoor cover. It is close to $300 but worth it . I've tried 2 generic covers before I finally ponied up for the factory Porsche one and you can definitely notice the difference in both materials, fit, construction imo. It also comes with a nylon covered steel braided rope and lock. The only thing I did to mine was to put duct tape over the "Porsche" logo as to not attract thieves.

If you do end up going with a generic one, make sure it is "water proof" and not "water resistant" if you have rain or snow where you live. Most cheaper "water proof" ones are of 1 ply construction meaning you'll either get scratches more easily and/or the cover will not let the paint breath properly. The best ones have the 3M mult-ply material on it.

 

Check out:
http://www.automotion.com/car-cover-for-porsche.html

 

I think most folks would agree you DO NOT want a water proof cover. You want a cover that will breathe. Trapped moisture under the cover can damage your finish at the least.
Covercraft is pretty much the industry standard for car covers. They also use very high quality fabrics. They've been around for a very long time and their custom fit covers fit perfectly. There's a reason why Mercedes and BMW use them as factory supplied covers. Not sure about Porsche.
For outdoor use Noah fabric is pretty good. I understand there's also another fabric above that. I think it's StormShield or something like that.
You've got a beautiful car, don't waste your money on a cheap cover. Invest a little bit in a good cover and you'll be glad you did in the long run.
Oh yeah, the factory covers are good too but $$$'s

 

I've used covers from a company called California Car Covers for my cars and bikes. High quality custom covers, suggest you check them out.

http://www.calcarcover.com/default.aspx