To make one from scratch is the same as making the model. It will take time, patience and a lot of trial and error.
Allen is correct, the first place to begin is with DPed. In it is the "How to" doc. It explains what each part of the DP file is.
First start with the boxes. This will give the frame work that everything else will work with. The Boxes should line up with the model. If you are making a model or working with someone who is then the source file will be your reference. Other wise I suggest exporting the model with MCX as a 3ds then importing it into Gmax. An alternative would be ACM. This will give the model in a 3d view. From it you can get your measurements.
Next will be the parts and to that the damage points and effects. Make sure you have an up to date list of effects to work with. You may need one for each era that you want to work in WWI, WWII and Korea. There are some that are common but each has new effects. I have a master list if you would like a copy.
Then will come the Gunstations and Hard points.
With DPed all of it will be placed in the correct order. Some editing in notepad may be required.
If you wish, you can use a default DP and edit it with DPed. You will still have to resize the boxes and change some of the data. I find it still takes about the same amount of time either way.
Let us know if you need any help
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