Kit bashing questions: Cutting prepressed parts

I am thinking about bashig some kits and creating a unique structure from them. I will need to cut some prepressed parts in order to to this project. Can anyone offfer me advice on cutting pressed parts? Looking for proper proceedures, tools etc.

I can only speak from experience with HO scale but I would think that the techniques I use would apply to almost all scales. I use a razor saw used mainly to cut track. Also, a # 11 blade and straight edge such as a ruler would be helpful. Measure 2 or 3 times and cut once! Jewelers files will help clean up rough edges. I tend to add wood parts from Northeastern Lumbar and Grandt Line parts such as doors, windows, etc. Also, changing the roof material such as, Campbells shingles, rolling roofing (cutting out construction paper and gluing it to the roof and then painting it, or painting a roof and using textures such as fine ballast. Have fun!!