To build:
makepkg -CcfLsr
That is -c for 'clean after succesful build', -C for 'remove $srcdir before
building', -f for 'force rebuilding if package already exists', -L for
'save a build log', -s for 'install missing dependencies using pacman', -r
for 'remove any installed dependencies after build'.
To create the .SRCINFO:
makepkg --printsrcinfo > .SRCINFO
Update SHA512 sums using updpkgsums from pacman-contrib:
updpkgsums