Your employer may most likely make you do work in this building.1) First, unless your allergies rise to the level of being considered a "disabiility," the employer does not need to make any accomodations for you--that is, they are under no obligation to do anything, no matter how small, to accomodate or amelioriate or mitigate your allergic reaction. To be a disability, a physical or mental condition must  substantially limit a major life activity (such as walking, talking, seeing, hearing, or learning)--most allergies would not qualify.2) Even if your allergies did qualify as a disability, the employer's only obligation is to provide a "reasonable accomodation" for *that* job. A reasonable accomodation is a change in how that job is done, or the provision of some assistive technology or device, which both lets you do the job and which is not too expensive or disruptive. The law does not, I believe, require an employer to transfer you to a different work site or location, or give you a different position, so if that's what it would take to "accomodate" you, I don't think the employer has to do it.