Anyone know how I can build a keypad for my arduino project? lets say 8 buttons... maybe use i2c interfacing?
If io is not an issue then I recommend you wire individual tact switches to their own pin and to ground. Then use inputPullup to have them pulled high by the internal resistors. They will read as high unless pressed in which case they will be low.
If you don't want to use any external ICs, the best way to have more than 5 buttons would be to implement a matrix keypad. For this see:
Arduino Playground - KeypadTutorial
If you are fine in using an external IC, see:
Arduino Playground - I2CPortExpanderAndKeypads
For 5 buttons or less, the answer provided by kidiccurus would be the better option
