It's taken me ages to figure out how to do the front end, though (using a different picture):
I've got that down to mean this:
But I can't fit the lamp thing in between the blocks in the Digital Designer.
I was wondering how you'd go about extending it for a full boiler earlier, then I realised that you can just add more of those bricks with the studs on the side to the free studs on the 2x3 flat brick
I'm hoping it'll end up being of a similar size to the old "My Own Train" models, but a bit more professional looking. Still trying to do a model from the picture in the OP, y'see.
This thing:
There's no green cheese bricks in the LDD, either, so I'll need to pick those up from 1001bricks or something.