I do not believe obelisks are the solution here. Trellis might work for cover and for a framework for your roses or climbers. Anthony de Grey is a specialist in strongly constructed architectural trellis in Scandinavian redwood from sustainable sources. There are five ranges, with eight lattice options, available in over 100 different colours. The construction is modular, and panels from different ranges can be combined. You should also consider willow or hazel trellis available from Chairworks which could also successfully screen your garden.