Select a location for your gazebo within the limitations of your property. Measure out the square footage of your gazebo with respect to accessibility while taking precautions not to overcrowd your backyard.
Create a design for your gazebo by making a rough sketch of how you want the finished structure to look. If you don't have a design in mind, you can find websites online that offer plans free of charge. You may also visit your local library for a selection of blueprints.
Dig out the vertical support footings. Use a post-hole digger to excavate the footings to a depth of 18 inches. Position the vertical posts in the footings, keeping all of them equal in height. Fill each footing with ready-mix concrete and adjust the positioning as needed by using a level. Make sure each post is properly aligned vertically before allowing the cement to harden.
Measure and cut the cross-bar joists and headers using a hacksaw. This will be determined by your design. Weld these to the vertical posts at each attachment point, checking for any signs of weakness. You may also wish to add a unique design to the top of your gazebo at this stage.
Measure and cut the rails to coincide with the number of posts. Position your rails at a height you are most comfortable with. Mark and weld the rails to each post, being certain to allow one rail-free section for access. If you prefer an open design, the rails can be eliminated entirely.
Prime and paint the gazebo as desired. This will depend on the type of metal used. Wrought iron rarely needs a finish coat, while aluminum and most types of steel do.