I'm thinking of having one but I wanted to see a sample so that I'll have an idea how to write mine. Also, does it have to have the same size of the invitation card? What type of paper/card is ideal for that?

Thanks!

Any size you like... it justs depends on how much information you want to have. You could have an A5 booklet with a thicker cover and normal pages inside and staple or tie a ribbon to hold it all together. Or just have a single card and print on both sides of it. I don't think its important that it be the same size as your invite... just whatever suits the amount of text you have.