I am new at cake decorating. I have been asked to decorate a 10" or 12" cake for a friend at work for a birthday party. I will be decorating it simple with buttercream icing and some roses on top and c shape scrolling on top and sides with a ribbon ( icing) border. It is not real time consuming but I just have no idea how to charge for my cakes.
I would appreciate any input you can give.

I would recommend you find some pricing from you local bakeries and set your prices that way. Doing that will give you an accurate guide based on where you live. The same cake is going to be priced completely differently based on the city/state. HTH.

Yup, I would agree with ddiagle. You also need to figure out your cost and what your time is worth. Doesn't matter if it is a 'simple' cake with just some roses and scrolls, your time is worth something. Plus it costs you every time you turn your oven on or run the water to wash the dishes (or dishwasher). Is it scratch or box mix? You will need to determine your out of pocket costs then come up with a price.

There are a couple of different price matrixes listed on CC. They can be confusing, but they will give you an idea about costs per (eggs, oil, etc).

hth