If the horse is over 4 years old, you don't necessarily have to start over fences by lunging. Lunging over fences is difficult to do well and correctly without a round pen and the correct type of standards. I see it done badly/dangerously way more than I see it done correctly or well. If you do anything other than a single low fence, you need to *really* understand striding and distances, but that's true for undersaddle work as well.
I started a lot of horses over fences from the saddle, no lunging over fences first, with no issues. If their foundaton is sound (meaning they are straight, forward, in front of your leg and obedient) start by trotting over single poles, then a series of trot poles adjusted for their comfortable stride, then at 2X the distance of the trot poles, set a little pyramid of poles (the gap in the distance is to allow an awkward green horse to engage his hind end without stepping on/rolling a pole.) Gradually raise the pyramid of poles to a cross rail.
When your horse can jump a crossrail after the trot poles and land cantering without fuss, build a little one stride gymnastic. When they can handle a little gymnastic without fuss, you can start jumping low single fences from the trot.
If you have not started a young horse over fences before, I would HIGHLY recommend you approach everything in a balanced two point, grabbing a piece of mane. Greenies take some big, unpredictable leaps, and you don't want to discourage them by getting left or getting them in the mouth.
I looked around for a good reference book or website for you and was disappointed at the lack of info. I did find a terrific series of articles on the USEA website that might be helpful: USEA - Starting Your Green Horse Over Fences - Part II
Of course, all of this goes better and easier with a knowledgable person on the ground, and the best thing would be to work with a trainer with experience starting horses over fences to help you and the horse, but I'm guessing if that was available to you you wouldn't be posting. Do have someone on the ground to help you and watch, it's nearly impossible to do on your own.