Hey there. I designed my own invites and am still working on all 200 of them! =P Here is what I did: If you are creative enough to come up with an idea from scratch out of your head, good for you! But I needed a little "inspiration" because there are so, so many things you can do.
Once I found a picture of an invitation style that I liked (by using google image and searching through hundreds of invitations), I started working on modifying it to fit my own liking/personality. I changed a few things up, adding some things I knew I wanted in there, and then it was time to make a sample before I made a final decision on the invitation.
So I bought just enough materials to make one invitation, and got opinions on perfecting it from family and friends. I was glad I made a sample because I did end up changing a couple things, so it was nice to not have all that money wasted.
Then I bought the materials and I've been working on them since. Not sure how specific of an answer you were wanting, but I'll give you mine: I did a background of black cardstock (Hobby Lobby), and added a smaller piece of white cardstock on top (Office Depot) using a scrapbook adhesive (Hobby Lobby). So before I attached and cut them, I just took the white cardstock and printed the invitations 2 to a page on the white. I used microsoft word to design what I wanted....I even added a picture! Then I have a polka dot scrapbook paper (HL) sitting across the middle of the cardstock attached with a small ribbon tied on using a hole punch. The picture was underneath the polka dot paper that is across the middle, so I got a circle paper shape punch from HL and punched a circle in the polka dot paper, so that our faces in the picture show out from the circle.
I hope this makes sense, and further, I hope it helps you any. I just got everything from Hobby Lobby craft store, except the bulk pack of white cardstock from Office Depot. If you want more specific info, I am very willing to help, so you can just email me.
Congrats on your wedding! And good luck making these invitations. I respect any DIY brides because I know first-hand all the work that it takes.