Im getting ready to add some doors and windows to a building and wanted to know what size balsa strips to make accurate scale wood trim around the windows and wood slates to make up the doors. One other question what would be a good material that I should use for glass for the windows

It really depends on what scale you want to build your buildings. Best bet would be to go to a DIY store and measure the width of lumber that would be used for the application. Then divide that by 35, 48, or 72 or whatever scale you want. That will give you the width you need to trim your strips to. Hope that helps.
Mark

When it comes to scale of doors and windows it is all relative... More info is really needed exterior, interior, what kind of building?