In Material Design language, floating action button (FAB) can be placed anywhere. You shouldn’t limit your creativity , even though Google guidelines recommends to use it on the bottom corner. Popular design blog Abduzeedo is a great example of this:
You can read full story about Abduzeedo Material Design app here.
If you decided to go for the top corner,- this brilliant FAB menu concept by thanksbnthanks shows how it could be done: