Some properties have drainage, power, gas, cable, telephone or environmental easements that will limit what and where you can build a deck. This information should be included on your property survey. In some situations you can apply for a variance or permission from the proper authority but this may take some time and or money. If you live near wetlands or a shoreline there could be restrictions on creating hard surfaces that will increase storm water runoff or disrupt the soil and cause erosion damage. Easements are fairly rare on most properties but they can exist without the knowledge of the property owners. Sometimes the landscape can provide you with clues like the presence of storm drains in the back yards or the location of electrical power boxes. Your neighbors are probably in the same situation as you, you may want to check out what they have been allowed to build.