Where are schematics in fallout3 and what do you need to build the weapons?

Where are schematics in fallout3 and what do you need to build the weapons?
basically:
schematics are instructions (blueprints) for how to create a new weapon from scratch.
look in you pipboy and, under notes, it'll show you what you need to build that weapon (eg rocketlauncher or dart gun)
then you need to collect those items, go to a workbench, and then create the weapon = WIN