The following shader allow buildables to be constructed on the surface BUT the bullets don't pass through :/
textures/pulse/base_section_clip
{
surfaceparm nolightmap
surfaceparm trans
// surfaceparm playerclip
surfaceparm metalsteps
surfaceparm nodraw
}
in fact, the problem is surfaceparm playerclip. Without this flag, buildable can be constructed on the surface