These excellent articles give detailed information on requesting reasonable accommodations in the workplace:
Asking for Accommodations under the ADA by Betty Kohlenberg, M.S., CRC, ABVE. This article discusses why you should ask, when to ask, whom to ask, how to ask, and what to say for a reasonable accommodation under the ADA.
Talking about your Disability in an Interview; Deciding to Disclose Your Disability by Betty Kohlenberg, M.S., CRC, ABVE.
Fact Sheet Series: Ideas for Writing an Accommodation Request Letter By Linda Carter Batiste, J.D. This article is on the Job Accommodation Network (JAN) site.