This is essentially just a box framed from some of the cutoffs remaining from the other parts. I started out with thinking I would just go with a flat roof but it really didn't take too much more effort to build in that slightly sloped front and sides.
Layout the footprint of the roof tier extension. I just spaced it out with the width of the 1x2.
Cobble it together. It didn't look high enough so I added the 1x2 to the thickness. I guess I could have turned the base pieces on its side to build but it was an afterthought.