Building a gate is a difficult job for most people. I recommend that you use a steel gate _frame_ kit. I makes gate building easy and sure. Some gate _frame_ kits come with all the hardware and some do not. Most gate kits will utilize a cable in tension top hinge side corner to the bottom of the opposite side to help keep the gate from sagging. This will help for a short time, but the real answer is to purchase a steel _frame_ gate kit that utilizes solid bracing in both compression and tension (corner to corner in both directions. If you need more information about this please let me know.

Gates need to be strong here in Temecula because of those darned Santa Ana winds that come through here each fall. I've seen fences end up in the neighbor's yard up here. Brick always helps, though it's expensive. I used to live in Chicago, and there were some chicago masonry contractors there that insisted in using brick. Job security, I guess, but in the end, homeowners were happy that their gates and walls withstood the elements.