We could help you far better if we'd know what exactly the door should look like.
A glass door can be everything from a regular door with glass window in it, to a door completly made of a glass plane.
I guess you're aiming for the 2nd one.
By the way, do you know what's the average size for a door texture?
Again this depends. You can even make a 16x16 piece of texture if you don't need any details on the surface such as dirt, scratches, finger prints or even refraction stuff.
A clean and plain glass door doesn't need to have refraction, you won't recognize it anyway, but it would eat up performance and might cause some visual glitches e.g. with tranlucent models behind it.
I'd use a dark, allmost black base color with a little color tint (slightly green for glass, slightly blue for plexi-glass).
As for the alphachannel, i would choose a 25-50% grey at first and tweak the intensity later on.
(should be even possible by using the $alpha parameter)
Since you're going to use the texture on a brush, LightmappedGeneric is your choice.
Also a cubemap is a must.
You're able to tweak the intensity and even the color of the reflection with $envmaptint.
Here's a template, feel free to use and edit it.
"LightMappedGeneric"
{
"$baseTexture" "yourpath/yourglasstexture"
"$surfaceprop" "glass" //determines the sound and decals when player shots object or walks on it
"$translucent" 1 //uses the 8bit alphachannel of the basetexture for tansparency
"$alpha" .5 //change the transparency. alphachannel of 50% and alpha value of 0.5 = 25%
"$envmap" "env_cubemap" //enables reflection using cubemap entities
"$envmapcontrast" .5 //contrast of the reflection
"$envmapsaturation" 1 //saturation of the reflection
"$envmaptint" "[.8 1 .9]" //tint the reflection using [R G B] values, also possible to lower the overall reflectivity by using
//lower values for each chanel e.g. [.5 .55 .45]
}
