Many fabrics can be used to make coats. First take into consideration the purpose of your coat. Is it going to be a winter coat to keep you warm, or is it going to be a light jacket to wear on cool summer nights. Some suggestions are: light weight cotton, denim, corduroy, light weight wool, wool blends, silk, rayon, and velvet. Sewing coats and jackets are both fun and practical. During cooler months everyone needs jackets to keep warm. Sewing coats can be challenging. I do not recommend even the easiest of coats for a brand new seamstress. The easiest type of pattern for a jacket would be one that does not require a lining. Another suggestion would be one that does not have sewn in sleeves. Also one that does not require buttons, or zippers.
A difficult type of pattern would include patterns that have difficult collars, zippers, many buttons and button holes, fancy trim, and things of that nature.
I would have to say that coats and costumes would be the most expensive type of clothing to make because they require more fabric and sometimes layers of fabric. Most coats require thicker fabric for keep warm with, which is usually more $. Cloaks are awesome and fun to make and maybe not as quite as expensive. They are also easier to make.