Aluminum is probably the best lightweight material to make a frame for a gazebo. You can even get Durawood brand which is aluminum coated to look like wood. EZ-up type canopies are really lightweight, with umbrella type canopies. A strong, pressure treated lumber should be used to construct the posts and frame of your gazebo. Cedar is the most popular choice. For the foundation, it is best to set the post frames into a slab of concrete, though a bed of rocks or gravel can serve for this purpose. For the roof, you have a wide variety of choices, from shingles, to siding, to shakes!