Do you have cower installed? You will need binutils but it is better to have the entire suite for building software from source called base-devel
If not
% sudo pacman -S cower base-devel

% cower -d sublime-text2 
% cd sublime-text2
% makepkg
% ls -al
% sudo pacman -U sublime-text2-2.0.2-1-x86_64.pkg.tar.xz
% sudo pacman -Ql sublime-text2 
% subl

(you may want to edit your /etc/makepkg.conf to set your prefferences , I use xz and comment out the line with facebook's spyware zstd I also add -T0 to the xz configuration to make it faster if you have 4cores/threads you may want to use -T3, leave a core for anything else you are doing while building a package - if you have makepkg.conf as default the above may end up in zst instead of xz ... so install whatever it is built)

The source in PKGBUILD says url="https://www.sublimetext.com/2"

So no need to add the repository directly, AUR seems to be maintaining the latest version at all times.
as regular user
% pacopts aur -I sublime-text-nightly

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