A quick tutorial on how to scale brushes for use in 3D skyboxes. This tutorial assumes you have prior knowlege on how to create the 3D skybox.
First off build the structure you want scaled. For this tut, I will be using this building:
Next select everything, hit ctrl+m to open the Transformations window. Set the mode to scale, and use the value ".0625"* for the x, y, and z values. Your screen should look something like this:
Click 'OK' and your building will now be scaled accordingly. You can now add this into your 3d skybox, along with scaled props and an env_cubemap. The finished product:
*The scale value, .0625 relates to the value set on the sky_camera. If you set the scale value on the sky_camera to anything else, divide it by a hundred to find out what value to use when scaling your building.