Add many sensors

I want to add 4 IR sensors and one sonar sensor to my ardupilot 2.8 fight controller board.How can i do it.

There are many ways to add sensors:
For example, the Sonar (depends on the models) can be directly connected to the FC and be used for altitude hold.

For many sensors, you can use an Arduino to collect all the sensors signals and transport these values as a related MavLink message using I2C or UART .

The question you must ask yourself is : How the Flight Controler will handle these signals ?
You need to get this information processed in a usefull manner, please consult the wiki for more information: