Welcome to ATP, Turtle!
As Rick said, there is a significant difference between what is sold as "chili powder" and what you will get by making ground/powdered dried chilies. If you're only using dried chilies, what you get will more or less -- depending on what kind of peppers you use -- approximate cayenne pepper. Chili powder, on the other hand, does include other ingredients. So, basically it just depends on what flavor you're looking for.
Here's a pretty simple recipe that I found on Food.com :
1/4 cup sweet paprika
1 tablespoon garlic powder
1 tablespoon cayenne pepper
1 tablespoon onion powder
1 tablespoon dried oregano
2 teaspoons ground cumin
1. Place all ingredients in a small container with a tight-fitting lid and shake to mix.
2. Store in a cool, dark place.
And, of course, you can vary the ingredients and amounts according to your own preference!
