How do I make PKGBUILD to install to fake root before makepkg builds

I have a tree which I need to install with a foder named /usr. This folder exists in src folder. Now I need to write a function in PKGBUILD that installs to the fakeroot before the *.pkg.tar.gz is built. What needs to go in > PKGBULD package() { # I need to copy the 'usr' dir in 'srcdir' to PKGBUILD's fakeroot }