Try calling the local Zoning Office at the town hall. Give them the address of the property and ask them what are the setbacks that are required (that is the distance from the structure to the property line)as well as any restricitons for the neighborhood. Once you have the setbacks you will be able to take rough measurements that will give you a good idea if you have the space and you will also know if you have any other restrictions. Then and only then will you have to hired a surveyor (and yes you will) to draw out the propsed addition on the site plan.
Hope this helps/
or directly at 585-279-8217 or lastly by email: Sal@SalafiaSOLDTeam.com
Web Reference: http://www.rochesterhomelocator.com