Create Quick Reflection Maps:

When creating realistic 3D buildings, it's best to begin with a texture map that is free from harsh reflections. Texturama buildings are cleaned of reflections, so they are the best to use. I'll show you how to create your own reflection masks below... it's very quick and easy to do once you learn my quick method.

Here is a sample image and reflection mask (to be inverted in 3D software).

Properly reflecting glass within your 3D scene:
(Note that the reflections move as the camera moves through the scene)

When using masks correctly, only the glass is reflective.

In your 3D package, use the two map images in the following slots:

Diffuse Color: 100% use Image
Specular Level: 50% use Mask Image
Glossiness: 15% use Mask Image
Bump: 5% use Mask Image
Reflection: 100% use Raytracing, then use Mask Image as a Mask, and make sure you use the INVERT checkbox (so that the black flips to white and white flips to black).

Sometimes I use the Mask Image in the "Opacity" slot as well so we can see into the building.

Creating a simple reflection mask:

Start by opening the building image in Photoshop: I've shrunk this image down really small for the purpose of this tutorial.

Now create a new layer so we can draw our mask on top of the original:

Click the rectangular marquis from the tools pallette and draw a large rectangle over each window section (one large rectangle per storey). Then fill with 100% black.

Now make this layer 54% transparent so we can see the window mullions through it.

Working on our rectangle layer, now we erase using the eraser tool with 100% strength and without a soft falloff.

Choose the eraser size which is close to the width of the window mullions (right-click in your workspace to summon the eraser pallette, choose and then hit your numpad enter button). Just take a wild guess at first, and if the brush is too large or small, use the bracket keys to re-size the brush "[" makes the brush smaller and "]" makes it larger.

Repeat the erasing process for each mullion on this storey until it looks like this:
(Be sure to increase layer's opacity back to 100% before continuing).

Now duplicate this layer twice and paint or erase any subtle differences which might occur from storey to storey. After you duplicate a layer, you can hold down CTRL before moving it - this will ensure that the windows remain aligned from storey to storey.

This copy seems to line up nicely.

And so does this!

Saving Out your Mask Image:

Now you can save your work as a Photoshop file to keep in case you'd like to make changes later.

Before saving your Mask, be sure to hide the Background layer. Now Save A Copy, and use JPEG format. JPEGs are nice for black/white images because they keep a small filesize. I usually add an "A" at the end of the filename to denote that it is and "Alpha-type" image.

Now apply to your 3D scene using these settings:

Diffuse Color: 100% use Image
Specular Level: 50% use Mask Image
Glossiness: 15% use Mask Image
Bump: 5% use Mask Image
Reflection: 100% use Raytracing, then use Mask Image as a Mask, and make sure you use the INVERT checkbox (so that the black flips to white and white flips to black).

And it should look like this on simple boxes:

And if you like, you can add a crown or cap to the building to give it a little more "design-reality".

Just for your knowledge, this is how the computer interprets the Inverted Mask:
The whites reflect, and the blacks do not.