Just like in the case of field plans, good old Paint is the solution for 3D plannings, too. First paint a domino from two angles: looking at the long side or looking at the shortest side (see picture). The next step takes quite some time: Use these two templates to create a simulation of a wall. You'll of course be faster if you copy and past the parts. Once you've reached a certain size, you can simply do that with a whole block. So go on like that until you've reached the size you wanted. Then save that picture and close the programme. Open the saved image again and save it with a different name. Like that, you have a planning template that you can use over and over without having to draw all the parts from scratch every time.
Now any pattern can be painted on that template. With a programme that allows you to lay another picture on top of this one transparently, you can simply trace the picture through. That isn't possible in Paint anymore though. That's why the planning of walls is so tricky - you have to do it all out of your head. I used this kind of planning in my Minecraft special that included a coal block.