Never saw a template. Most people just do it by Eye.
Search the tech forum and get an idea you like. Tape up the area with some wide painters tape and start drawing it out in pencil until you have what you can live with. Do both sides together and at the same time and they will be come out close.
Then cut 'em!
What style do you want? There is a half door thread with tons of different ideas.
I just got a piece of angle iron, clamped it to where the door meets the tub at the hinges and where it meets at the door opening to give me a slant. Then i followed the angle iron with a grinder and cut away. Then just used a thicker sheet of sheet metal to make the flat top.
Similar to what fasteddy did with the cap... If you did not want the round tubing, 3 in tubing will work PERFECTLY!!
I got some 3 in x 1 in 16th wall square (rectangle), cut it in half length wise and that gives you a really nice cap, it fits perfectly inside the main door body and makes for a cleaner and easier weld.
Also, I cut out the whole interior section and just re skinned the whole thing in 18 ga sheet metal and made an access panel for the handle part.
I don't have pics of the build on my I phone here, but in the first couple pages of my build thread there are pics of them in there. "Chicago builds a 40". It in the hardcore section.
Here's a shot of my DS that I have on the phone.
Not too telling, but it gives an idea.