Upper decks certainly require a safety feature to keep objects from going off of the edge, and heavy glass railing is a way to not only make the deck safer, but also improve the look of the deck itself. Glass rails are typically enclosed in an anodized aluminum frame, though some have rounded off and polished edges, called "seamed" edges.
The metal structure that will support the glass should be created first. It is most cost effective to design the metal framework prior to ordering the glass panes that will fit into it. If possible, keep as many of the glass panels to the same size. This will save the glass company from having to custom make each panel, and it will also be easier for installation. Make sure the panels are slightly smaller (1/4-3/8 inch) than the distance between the inside of the vertical frames, to allow for easy fitting.
Install the baseplates to the deck itself according to your initial design. Use the heaviest grade of stainless steel screws that will fit through the baseplate holes. Check your measurements often, as much as 1/8 inch difference can be problematic when working with glass panels.
Install the uprights and bottom channel. The bottom channel holds the glass up, and the uprights keep the glass panels from moving from side to side. Use stainless steel screws to hold the uprights and channel firmly in place. Make sure no screw tips are visible on the inside of the upright or bottom grooves where the glass will sit. Glass is very strong, but one little scratch with a screw can render an entire pane dangerous. Place felt or urethane pads over each screw attachment location, or any other protuberances.
Carefully lower each glass panel into the grooves on the sides of each pair of uprights. The glass should fit snugly down into the bottom channel. Do not force the glass into place. Do not tap it into place with anything, but lightly jiggle the pane until it settles into place. There should be a gap on each side between the aluminum extrusion and the vertical edge of the glass of about 1/8-1/4 inch. This will allow the deck to move during the year, and not end up with a cracked series of glass panels.
You may want to put another piece of extrusion/molding on top of the glass to keep it from chipping. This should be cut to be ¼-inch smaller than the width (from left to right) of each panel. Attach the top rail pieces using silicone exterior grade clear adhesive. A caulking tube is the easiest way to keep the top rail secure.
After the silicone has cured, about 48 hours, you can clean the glass with a commercial cleaner and a rag, or a squeegee. It is a good idea to use a commercial cleaner at least every two weeks to keep hard water build up from forming on the clear panes.