Suggestions on how to keep an indoor cat indoors?

So, my cat Nero escaped onto the roof, through a screened door. After about 45 min, and a can a tuna, I got him inside. This is not the first time. I'm surprised my neighbors didn't call the cops on me as a suspicious person walking around behind their house, I live in an apartment and Nero insisted on staying on the far porch. He can get to the ground from there by jumping from the side wall to the stairwell. I don't want to let him be an indoor/outdoor cat, even though the few times he has escaped when we weren't home he has come back. I've seen foxes, raccoons, and a couple other city wildlife, not to mention other cats, that could seriously hurt him. We're also on the edge of a major road, though surrounded by woodland. But, I'm at my wits end. I've considered closing in the porch with wire fencing, but I want to make it into a garden, and that will cut off more of the light, which is already in short supply, even though the holes are about 8 in x 4 in, just small enough to keep the cat from getting out (at least quickly, I have no doubt that a determined cat could get out of a locked safe). Does anyone have any suggestions? At this point I might try anything.