I'd go taller whenever possible and use guy lines for support. Yes, some varieties will grow taller than others but most can get 15-20 feet pretty easily if cared for properly. For example, in CastleHollow's picture, I think it would be just as easy and arguably more effective to either screw an eyelet from the peak of the roof and string lines down teepee style from there for the bines to grow up. Or, better yet, to add a pole from the peak of the roof anchored with guy lines to the corners of the house to extend it up even higher. Keep in mind that a healthy, mature plant will weigh a bunch toward the end of the season, and wind/weather will tax a PVC set-up quite easily, especially as you extend it higher and higher. People in wide open sapces without structure to anchor them often find two 8-10' galvanized poles coupled together make a more lasting and weather-withstanding option but again a lot depends on your particular set-up. Consider if there are anchor points on houses or patio covers or trees that would work to help support or extend trellises from. I recall someone posted pictures of a well-made, heavy-duty steel setup last year. And when a hurricane blew by, even it came down...don't underestimate the weight of your plants and their ability to catch wind. Having mature bines fall down during the course of the season sucks--it's even worse to string them up again! Forethought now, and building soon, makes a lot of sense for the new growers because it's shocking how fast these things grow come May and June.