beam size to replace wall

I am looking for an experienced contractor to help me with replacing a wall in my home. It is a wall that is between 10-20 feet in length and is currently made of wood. The purpose of the new beam is to provide structural support, so it will need to be sized appropriately to ensure that the integrity of the wall is intact. I need someone who can measure the wall accurately and recommend an appropriate beam size for the job. If you feel you have the expertise and knowledge to do this job, I encourage you to apply for this project.