I think what they do is break it into parts. For the door, select the faces you want and extract.
There is a tutorial on YouTube where a guy makes a mini.
Displacement maps are easy.
Graph your material in hypershade - select the very first node, and plug a file in its disp slot.
For any other bits you should just be specific so people could answer you better.
That's my 2cents.
You'r right. The door is pretty easy to be done with extrusion 
and I'll go for displacement on the other parts. Just another thing to learn, which is good, right 
?? thanks for the reply mate!