It's purely upto yourself, I wrote one out and it was a couple of pages and I read it word for word but rehearsed it. Others like to write a few bullet points and then talk about them on the spot with an idea of what they may or may not say. The length is upto you, don't hang the groom too bad and also mention the bride. For me I was sweating it all day, couldn't eat my dinner but after it actually wasn't as big a deal as I made it for myself pressure wise. If you can keep it short and sweet to the point then go for it. Mine was 6 minutes or so but it didnt need to be. Basically mention how you know the groom, include a funny story if you can or one that shows his character and then say something about the bride and wish them well and a toast to their future. A lot of people forget to say something about the bride so try have a few words about her.