hello.
I have developed a per pixel phong shader for render some architectural models.
The problem is that i think that for simple architectural models is simplest and fast use a simple shader with directional lights.
May be?
I read this article :link
and i ask if for you i can implement a light sistem of tree light (key, fill and back) with directional lights.
I would create somethings like sun.
thanks.

Having 3 lights instead of one can easily be done by just adding the light from each light source before multiplying with the diffuse color.

If you just want to show models without too much work, you can use an engine with light sources built in as an HLSL function call. Then you will get many types of light sources without any extra work.