How to finish this outside wall

[skeg0]

Our contractors have left this outside door way to our garden store unfinished. I will be getting a concrete block for the bottom part but not sure about how best to finish the walls. Its outside so will be exposed to the elements. 

it’s a timber frame build with brick surround so the inner wall in the picture is mostly wood. 
 

Any advice most appreciated!

[Onoff]

Why have they left it unfinished?

 

What was the original  plan to fill the hole?

[ProDave]

So basically they have not fitted the door and door liner?