I just went to a baby shower a few weeks ago where the invites were home-made. Very very cute--animal themed also.
A pair of craft scissors (that make wavy cuts) are your best friend. :)
What these invites looked like was this:
1) cardstock, same size as the envelope
2) slightly smaller piece of solid (different colored) paper with the details of the shower printed by computer in cute script, glued to the cardstock backing
3) patterned 1 inch trim across the top and bottom (this was a zebra stripe piece of paper cut with the craft scissors).
4) hole punch (2 holes punched one inch apart at the top of the invite)
5) 7 inch length of tan raffia, tied thru the hole punches into a bow, at the top of the invite.
I can't remember for sure, but I think there were also stamped (like with a stamp pad) hoof prints across part of the invite.
The outside envelope (just matching colored envelopes purchased at Micheal's) had baby wild animal stickers sealing the flap.
It was all very cute. The colors were chocolate brown and teal blue, for a little boy. Cute cute cute!