There are two main possibilities.
The first one is to make a GUI on the Arduino itself. Add a TFT screen, touchscreen if you want the user to interact, or a non-touchscreen (cheaper) if you just want to display. Then, within your Arduino code, you can display the temperature data, and if you go the touchscreen route, interact with the user.
I own a couple of Arduino Esplora devices, and they would be near perfect for this, as they have a non-touch TFT screen, a joystick, buttons and a pot. All the equipment you need to display the temperature. Oh, and it has temperature and light sensors onboard.
The second way would be to make a GUI on your desktop/laptop machine. In your Arduino code, you could send your temperature data through USB (Serial), Bluetooth (SoftwareSerial), WiFi, Ethernet, nRF, etc etc etc. If you don't mind having the Arduino tethered to your computer by a cable, USB<-->Serial is the easiest solution. The software on the computer listens on a serial socket and when it receives temperature data, it displays it within its GUI.