How does someone write a Royalty Free License Agreement for selling stock photography? Would I need to have a lawyer look over it?

While the normal response of a lawyer is to advise you to seek the assistance of a lawyer, you may be able to find help at your local library. NOLO has books that are pretty helpful to non-lawyers and have very good forms. Having said that, if it is royalty free, what does your reference to "selling" it?  I also assume that since you want the license it, even if for free, you are trying to protect your rights. Depending upon how valuable those rights are, you may want to have a lawyer's help.   The way I look at it, there are also self help books at the library to help non-mechanics fix a transmission on a car.  I might be tempted to try it on an old "junker" but not on my day-to-day transportation.  Sometimes it is worth while to pay a professional.