There are a few rules to this:
1. Make a post with [Claimed] in it if you are to add a part, so someone doesn't add one on before you do. Edit the image in when done.
2. Don't overdo in one edit. Add a barrel, an optic, some silly thing, just nothing huge that could ruin the fun for others.
3. Export as .png.
Here's an old example of a finished one. Contributions are best done in something like MSpaint or paint.net so everyone can easily add stuff on. No flashy effects with layers!
Here's a grip. Let's go.
