Off leash outdoor enclosures?

We recently moved from our 3br house with a screened in back patio to a 3br duplex with no sliding glass door or patio.  We do have a garage in the duplex now, which we did not have in the past.  Two of my cats tolerate being on-leash but don't enjoy it and end up miserable outside.  My other two I don't even attempt to leash.  All four cats severely miss going out onto the patio.  Any ideas or suggestions for an enclosure outdoors that is affordable but safe for them? Thanks! 

There are ideas here:

http://www.thecatsite.com/t/278747/cat-enclosure-pictures

http://www.thecatsite.com/t/277644/cat-enclosures

http://www.thecatsite.com/t/25947/cat-enclosure-new-addition

http://www.thecatsite.com/t/210517/our-outdoor-cat-enclosure

http://www.thecatsite.com/t/228224/moved-and-have-new-cat-enclosure

http://www.thecatsite.com/newsearch?search=cat+enclosure&type=35

I built my own from wooden posts and deer netting. I'd recommend putting a roof on the enclosure if you do this as really determined cats will find a way to climb out.

http://www.thecatsite.com/t/276982/moving-house-taking-the-colony-with-me-any-advice-please

Your cats all look so happy on their patio!

THank you! Those links are all very helpful. I'm going to get approval from my landlord first but I expect to be able to provide them with something before the end of the year.