What are the disadvantages of GPS surveying?

• Sometimes the GPS may fail due to certain reasons and in that case you need to carry a backup map and directions.
• If you are using GPS on a battery operated device, there may be a battery failure and you may need a external power supply which is not always possible.
• Sometimes the GPS signals are not accurate due to some obstacles to the signals such as buildings, trees and sometimes by extreme atmospheric conditions such as geomagnetic storms.

when you taking the elevation from bottom to top

The disadvantages of gps surveying in terms of construction of building is you can not used in setting out, levels of the actual construction drawing.