I need to build a gate this week and I was going to do make the frame out of 2x4s but then I thought wait, don’t I want the gate to be a light as possible? I have some 2x2s that I can use as the frame and cut the weight by more than 50%. Am I missing something? Is there a reason to build a big heavy gate?
Depends, what are you trying to keep in, or out?
A bull or a toy poodle?
How wide is the gate? Wooden gates are often made out of 1X4 or 1X6 lumber to keep them strong and light. If it’s very wide you’ll need a diagonal cross brace that may have to extend quite high on the hinge side, or various other bracing schemes. Is this a solid gate?
65 1/5 inches. Let’s say we need to keep an akita from bullheading their way out but isn’t that more about the latch and hinges and not the frame of the gate?
And Yes I was planning on a crossbrace to prevent sag
Here’s a website claiming free wood gate plans. I don’t know anything about them but there’s some good pictures, and maybe they do have free plans that will work.
Look at the bracing on the Cape Cod gates, and the Keel gate, that’s the kind of thing you’ll need for that kind of width if it’s heavy enough to be sturdy. You can make an open frame gate like that and cover it with wire or chain link fence to keep it light also.
And I’m thinking of making it a double gate so each one would only have to span 33 inches
By necessity, gates are only attached at one end.
This makes them more susceptible to buckle and bend than the rest of the fence, ergo they need to be stronger and better braced which usually means they need to be heavier.
And once it’s buckled, or hit and bent or people swing on it etc and it becomes difficult to open/close your neighbours will think “why didn’t he make the gate stronger the first time.” 
If the gate is crossing concrete, then you will need one of the gates to have a metal anchor post that can be let down into a hole in the concrete to fix the gates in place when closed (there’s probably a technical name for that thing, but I suppose you know what I mean). The other side, without the anchor post, is the one that would open most of the time.
If the gate is crossing dirt, then I would definitely sink a post in the middle for both gates to latch onto, rather than having them latch to each other, which would be a serious weak spot.
If you sometimes need the entire width to be available, as in driving something through that space, then I recommend making the sunken post removable, as with a concrete casing in the ground.