Thanks, Marty! Could your method be used on conduit also?

Conduit normally requires support on both sides as it is being bent otherwise it tends to go oval shape. If you bend it to sharply it will flatten out in one spot. Will work fine with rebar.

If i was making this i would use conduit instead of rebar. Use half or three quarter and the correct bender. If you want a long arc use the bender to make a series of short bends that blend into a long arc. Might take a couple of practice pieces before you like the way it looks. Or you can make a few sharper bends and make the sides and the roof lines flat, easier to bend. And there are all kinds of connectors for joining conduit together. Take a trip though your local electric supply, might give you a few ideas.

Don't know if this is what you want but it might be something to think about.

http://www.shedandshelter.com/syntheticcovering/syntheticcovering.htm

There are several plans made with short section of conduit and the tools required would be a hammer, drill, and a saw.

On a construction project where we have a considerable amount of rebar to bend in a common pattern we would find an expendable slab or flat piece of dry ground, calculate out a segment bend and use a dedicated rebar bender to put a few degrees of bend every few inches, don't use an electrical conduit bender because rebar is a lot stiffer than conduit.

We would draw out the arc we want and do a segment bend, a set number of degrees every so many inches. When we get close we would check it against the arc we drew and add or remove bend as needed. This works for less than perhaps a dozen pieces.

More than that and I would haul the rebar to a welding shop that has a roller bender. A roller bender is, in essence, a set of three rollers that you feed steel into to form a smooth bend. Most commercial welding and steel fabrication shops will have one. Half-inch, #4, rebar isn't really big by construction standards and rolling a consistent bend into it is pretty quick and easy. They might charge you a few dollars a stick. Transportation might be you biggest issue.

I have bent just one or two pieces in a one-off job by stuffing one end into the ground up against a slab or something solid, grabbing the other end, and forcing it into roughly the right shape by leaning into it. If it works your set. The problem is that your bends are unlikely to be consistent. Partly this is just the way of such log-cabin approximations but it also has a lot to do with the rebar. Rebar is usually minimally processed scrap metal and is very inconsistent. One part of a stick can be pretty hard and another, just a few inches away, very soft. Trying to bend the piece in one forced move usually means the soft spots bend and the hard spots stay straight.

Lacking an appropriate bender we have used a sledge hammer pounding the bar suspended between two pieces of heavy steel, the bumper of a heavy truck, or driving the truck onto the bar spanning a concrete curb. Anything to get a few degrees of bend. And then repeating this every few inches according to your segment bend calculations.

it can also be done by making a simple jig - 3 vertical posts in a triangle put the rebar across two of the posts on the INSIDE of the triangle, and take a jack and press from the 3rd post to the part of the rod between the other two posts (bending it out slightly, release, slide bar, jack, etc - it's the exact same principal of the "3 roller" benders that someone mentioned

Another slightly brutal method is to lay it across a couple of boards with a gap between them and beat it with a sledge or stand on it between the boards.
It is not quite as controlled as a bending jig but will get the job done.

Another way is with a hickey.
A hickey is like a big crowbar with a hook and a shoe on the end to grab the steel and bend it using the bar as a lever. The sho is usually separate and a steel pipe is the handle.
They are usually used for bending electrical conduit. You can rent them from tool rental places if you have to.

Here's another crude method that works.Dig out the Arc you are trying to establish,into the ground,then lay the rebar over the trench,& while someone is holding each end(with Leather gloves)Step on the rebar towards the middle,& kind of jump on it,until you acheive your wanted shape,also while standing on it in the center,have the other 2,at each end,push towards you,to acheive the arc,& should you pass your objective,it can always be pulled out,by laying the arc on the ground flat,& pulling from each end,kinda' like a Giant wishbone,until you reach your desired Arc.This method works,& is cheaper than a case of Ranier Ale! Good Luck

I don't think that the jig method would work with conduit as it tends to fold flat. a regular conduit bender might be better, but it won't make as nice an arc - it would be lumpy.