Arduino Uno project_Temperature Control System (computer organization)

Fans are the most common form of cooling for modern electronic devices today, which are very widely used to reduce temperature by actively exhausting hot air. In this project, we are to design a temperature control system which would allow to keep system temperature down to the one specified by utilizing fan as cooling device.
This is what's gonna happen:
1. If desired temperature exceeds current temperature then turn ON fan half power.
2. If current temperature exceeds (desired + 5°C) then set a fan to full power.
3. If current temperature exceeds (desired + 10°C) then alarm sound is activated.
4. If current temperature stays above (desired + 10°C) for more than 30 seconds than turn off the system LED.
In a being time fan stays ON. Once the temperature goes below desired one, system LED gets turned ON back.