A drone is an unmanned flying vehicle. Drones are used in war for surveillance and to attack targets, and in civilian territories by law enforcement officers to keep an eye on criminals, drug smugglers and illegal immigrants. Hobbyists also design DIY drones at home for recreational use, having fun piloting them and even shooting videos from high up above their neighbourhoods.
Determine whether you want to build a drone that you steer by remote control or one that will operate autonomously while being controlled by a on-board computer. If you steer it by remote control, you might rely on observing the drone in flight from your position on the ground or by viewing transmissions of streaming video shot by the drone's on-board camera to help you navigate the terrain. On the other hand, an autonomous drone will need sensors, such as an altimeter and gyroscope, to help it orient itself so you will need to take into account where you will place the instruments.
Sketch drawings of the type of drone you want to use. Your drone could be a helicopter or an aeroplane. A helicopter can ascend and descend vertically or remain hovering, while an aeroplane is good for smoothly cruising from one location to another.
Research how much weight a particular helicopter or aeroplane engine can lift. Subtract the weight of the motor itself to find out how much weight you can allocate to the plane or helicopter structure, radio controls, sensors and camera. You may have to increase the size of the aeroplane's wings or the helicopter's rotors, and use lighter material, such as balsa wood instead of plastic, as you balance weight and power requirements. A heavier drone may be sturdier and able to withstand gusts of wind, but be unable to remain airborne as long as a lighter drone that isn't as strong.
Prioritise items and features for your design; if you really want there to be a camera, pick one and add its weight to the amount you need to lift. If the motor you picked won't support it, you'll either need to get a more powerful motor or reduce the weight of the rest of the aircraft. You may have to work out multiple versions of your helicopter or plane to achieve the correct balance, and then test its performance through trial and error.
Place electronics and power supply in the fuselage of a plane to keep the weight balanced, and place the camera, if you are using one, in the nose or the cockpit. For a helicopter, the power and electronics will go in the helicopter body, with a possible camera mounted in the front.