I'm getting my wedding dress custom-made and I'm so glad I went this route. As a US size 16, and after watching my size 14 sister struggle to find places who even had things in her size to try on, and then settling for something at David's Bridal, I knew I was going to get a custom dress. Things NEVER fit me off the rack anyway and I did not want to deal with the aggravation.
Luckily, I have a lady who lives and works in my neighborhood who owns an alterations/custom gowns shop and she is making me the exact dress I want for $250 plus fabric! So cheap! I can't believe more people don't do this.
Tips for custom-made wedding dresses:
Know what styles work on your body
I'm extremely pear-shaped so I knew I wanted a low neckline, ruched waist, lots of structure up top to emphasize my small waist and bust, and a more flowing bottom to de-emphasize my wider hips and butt. Take a brutally honest friend and go to a store that has dresses in your size and try on different styles — but don't even think about wedding gowns. Find a garment construction that works for you and go with that style of dress. What looks good on me is going to look not as good on an apple-shaped girl and vice versa.
Be inspired by your interests
If you're a movie buff, geek, into fantasy, etc., look for dress inspiration, colors, and details from those interests. Here's a great example of a bride who was inspired by an anime she loved. It can be a subtle detail (golden snitch trim! TARDIS blue!) or something straight out of a storybook.
Shop around for a dressmaker/seamstress/tailor
Lots of people make custom gowns. Ask in your circle, check in Yelp, contact local theater companies (for costumers!), check online shops, and your local yellow pages. Ask to see some samples, pay attention to quality, look at the seams, ask to see photographs, etc.
Bring in as many photos as possible
This is to show garment construction, color, style, fabric, etc. Your dressmaker will probably have her own opinions on what will work fabric-wise. For instance, my dress would work in silk or satin, but wouldn't have a chance of holding up in charmeuse. Settle on what you need and go fabric shopping.
Be your own advocate for the fit
Be brutally honest at the fitting. If you don't like the way something is fitting, make sure they take note. You have to live with the dress, so now isn't the time to be shy for the sake of being polite. Bring an advocate with you if you know you'll have issues with this part.
Designing your own wedding dress can be awesome. Stretch your creative muscles and enjoy the process.
Going the online route?
Here are some tips for Etsy: