Odering a window
Generally, when asked to do a custom piece, I like to visit the site where the window will be installed. In this way I can get a feel for the style of the home and see how the client's tastes run. Occasionally, I'll pick up a design idea from a piece of the architecture or some of the furnishings.
I'll also see how much light will be coming through and whether it is direct or indirect sunlight. Many people prefer cathedral glass (see the following paragraph) because it lets in more light and doesn't look as "heavy" as opalescent glass. But in direct sunlight, the color of cathedral can look washed out as if it has faded.
Opalescent or Cathedral?
The term "Stained Glass" originally referred to the silver stain fired onto the back of a piece of glass which gave it a color anywhere from deep amber to bright yellow. Now, however, it refers to any decorative colored glass assembled with lead or copper foil as well as to the sheets of colored glass themselves.
There are 2 basic kinds of colored sheet (stained) glass; Cathedral and Opalescent. Cathedral glass is glass that you can see through. The amount of the diffusion of the light can vary from completely obscure - where you can only perceive light and shadow, to glass that looks like clear glass with color. And while a lot of cathedral glass will appear to have no particular color without light coming through it, like when viewed from outside during the day, opalescent glass will show a color with or without transmitted light.
All of these factors must be taken into consideration when planning a Stained Glass window.
see also: http://www.homestudioartglass.com/your_window.htm