there are some rotation options above units on unit panel in world editor u must first close all this rotation options.(like says random rotation bla bla...)
Then select your building you want to place before placing it look at the prewiew window that shows the 3d model of your selected unit or building.
There is an option there that says rotate if you change the rotation values on prewiew image, before placing the building or unit you will see the ghost image on your mouse is rotating as well.