Celtx - Need guidance with first PKGBUILD

Question

Ok, I decided to make my first PKGBUILD, and chose Celtx (http://celtx.com/) since it seems like a very useful tool, and not too complicated. 
I already installed it manually and it works fine. However, although they state it's open source, the sources aren't available on their website...only language-specific compiled packages. Can I make a package for the AUR without sources?
Anyway, these are the installation steps I had in mind: extract tar.gz to the /opt directory --> create a symlink for /opt/celtx/celtx in /usr/bin --> copy the license to its appropriate folder (/usr/share/licenses/celtx).
I think that's it. Am I missing something or trying to do something I shouldn't? It seems simple enough and I'm working on the PKGBUILD, but I would still like to know if I should even finish it based on my first question concerning the lack or sources.

Answer 1

Oh well, I finished before getting a response. Doesn't matter...I'm just glad I did something, regardless of how inconsequential. 
If anyone wants to take a look at it below, and point out any mistakes, I would be grateful. By the way, it does work. I built the package and installed it with pacman, and everything is where it should be, and it runs. 8)
pkgname=celtx
pkgver=0.9.8
pkgrel=1
pkgdesc="Pre-production software for film, video, theatre, and animation"
url="http://celtx.com/"
license="custom:CePL"
arch=(i686)
source=(http://www.celtx.com/download/Celtx.tar.gz)
md5sums=('f59759e16b3d64e3592aaf37641ee5b8')
build() {
mkdir -p $startdir/pkg/opt/
cp -R $startdir/src/$pkgname $startdir/pkg/opt/$pkgname/
mkdir -p $startdir/pkg/usr/bin/
ln -sf $startdir/pkg/opt/$pkgname/$pkgname $startdir/pkg/usr/bin/$pkgname
mkdir -p $startdir/pkg/usr/share/licenses/custom/$pkgname
cp $startdir/license.txt $startdir/pkg/usr/share/licenses/custom/$pkgname/