Frame Rail guide?

[Kochiro]

I am building a custom rig for my first 1/14 scale rig. It is not based on any available kit so I have decided to buy just the parts I need rather than modify an existing kit.

I have purchased a blank set of frame rails but my question is where to drill all the required holes. I haven't seen any guides online for where to drill so how do you guys that are doing custom rigs know where to put the holes?

Thanks,
Jay