Belly Dance Bra Bases
If you want to make your own belly dance bra - one that looks good AND fits properly - then finding the right base is 90% of the battle.
Sure, you can buy a ready-made costume bra and tweak it, but no amount of tweaking will ever get it exactly right - especially if you are larger than a D cup. Belly dance bras are made in a very basic range of sizes. Transforming a lingerie bra isn't easy - but the fact is, there's much more science behind their sizing and therefore a much better chance that they'll fit you better. Shushanna has some great advice on how to choose an everyday bra that's suitable for embellishment.
The trouble is, if you can't find a bra that passes Shushanna's cherry-bowl test (and it's getting more difficult as lingerie bras get softer), you're going to have to stiffen it with plastic mesh or buckram, which is a fiddly job. If you can't face that, then the other option is to buy a professional belly dance bra base from Egypt on eBay:
Of course, these bra bases are sold in a few basic sizes and are unlikely to be a perfect fit - but at least they are easy to cut and adjust, unlike a bra that has already been covered and embellished. And they're cheap enough that you can buy two or three and experiment!