i have someone who wants elmo on a sheet cake. How in the world do i do this??? Never done anything like this before

Go to the galleries and do a search for elmo. I just looked and there are 28 cakes for elmo it may give you some inspiration.

I am baking a 3/4 of a sheet cake a placing the elmo face pan on top. you can see a cake just like in the one in the gallery of photos. I am starring the bottom and free handing the top to make it look like a furry monster.

I made an Elmo cake for my 2 year old's birthday earlier this summer. I just made a sheet cake, then piped my outline of Elmo and filled it in with stars. If you aren't comfortable with freehanding it, you can cut out a picture and lightly lay it over your cake once the frosting has crusted a little. Then pipe around it, CAREFULLY take the paper off, and fill it in. A lot of people like to do buttercream transfers, but I haven't tried this yet. (Someday...)

I just did my daughter's b-day cake with a strawberry shortcake pan over a sheet pan...17" pan. I placed the ss pan over the sheet pan to make sure i got the right size so that it would fit.

After baking/cooling/etc, I frosted the sheet cake w/ white icing completely. I frosted the sides only of the strawberry shortcake cake with the same white icing. I placed a board on the top side of ss cake, flipped it over then placed it bottom side down on top of the sheet cake. Once that was done, I decorated Strawberry shortcake according to pan instructions and then decorated both the bottom and edges of the sheet cake as well as the joint where the ss cake and the sheet cake met.
This was my first character cake ever so it worked out quite well...it fed quite a bit - 25 kids plus 25 adults.

I hope this makes sense. good luck!!

I made a buttercream transfer (bct) of Elmo and put on sheet cake. I found pic on the internet and modified it. It was quite simple. Give the bct a try if you don't have Elmo pan.