Lattice on top of a deck rail is attractive and fairly simple to install. Build a frame of 2 x 4s the length of your deck rail and the heighth of the lattice you want. Tack lattice to what will be the outside of the frames. Use deck screws to attach the frame(s) to the railing and the side of the building. If you are installing it around the entire perimeter, you can attach the frames to each other at the corners. An additional 2 x 4 angled across the top from one panel to the other at the corner will add stability. After the 2 x 4 frames are installed, tack a second piece of lattice on the front (or inside) of the panels. Next, groups pots or line up deep window boxes around the perimeter of the deck. In addition to the morning glories you're planning, cannas, dahlias or bananas grow big rapidly and will offer privacy. You could also set out pots of tall houseplants like palms.