I would recommend getting more packs under your belt before advertising your services.
Keep building, maybe build for some close friends if they ask, and post everything here on the forum (and on Instagram and Facebook if you want). This community will help and guide you to making the best packs possible, and once your quality and consistency is up to standards people will start approaching you about builds whether you have a post up or not.
Building and selling a pack to a random stranger is a huge liability. If something goes wrong with the pack, even if it’s caused by misuse, that customer could ruin your life with lawsuits and possibly even criminal charges depending on how aggressive their lawyer is.
Be safe, be smart, go slow. Learn, watch, listen.
That’s my 2¢ anyway 
I wish you luck man.