2D Building Illusion

This Is a '2D' Building, if you have seen these before, you will probably know how they work. if you have not, jump down the post(:

This building is actually 3D, it just looks 2D when viewed at at a certain angle.
The solution is is that the building is actually triangle shaped. if you are viewing it at a birds eye view, the side you are looking at in the pic above is the bottom of the triangle.
it didnt take me long to figure it out, but it might just be because i have a very keen eye(: