You really don't want to run the wire from the temperature sensor any substantial distance - just enough to get it away from the heat generated by the Pi itself. Get it converted over to digital data (assuming it isn't one of the I2C devices) as soon as possible, and use something like ethernet for fast reliable lossless long distance transmission - analog sensor readings will be substantially affected by cable length and even I2C is only good for a few meters. FWIW, for a somewhat different application (a weather station / home automation control panel), I'm using an Arduino shield (a WxShield, http://www.osengr.org/WxShield/Web/WxShield.shtml
- its scope extends beyond what you need, it also listens to 433MHz remote temperature sensors) that uses a Sensirion SHT15 temperature/humidity sensor on the end of a 3ft cord to get it away from the hardware's heat (the Arduino continually reads the sensor and sends the raw data over USB to a Pi, which decodes/translates the data into human-readable form and publishes it to an in-house MQTT broker).
There are off-the-shelf remote temperature sensors (from Oregon Scientific and others) that will take readings every minute or so and broadcast over 433MHz, and there are various maker projects out there to read them (the protocols were reverse-engineered some time ago), for both Arduino and Raspberry Pi. For these, 100ft straight-line range is not out of the realm of possibility, but if you've got a lot of earth/etc. in the way, then reading a local sensor, converting to useful data and sending over ethernet would be a much more reliable approach. The hardware next to the sensor doesn't have to be a Pi, but the ethernet port built into most Pi's simplifies things.
Note that most of these sensors don't read out in celsius or fahrenheit, the raw data needs a lot of massaging to turn into the numbers that humans want, and that can be tricky for the most accurate results. Seek known good code for this.
Adafruit has a couple of nice I2C-based sensors, the Sensiron SHT31-D (https://www.adafruit.com/products/2857
) and Microchip Technology MCP9808 (https://www.adafruit.com/products/1782
), along with sample code. You'll find most of these lean towards Arduino implementations, but many can be (or have been) ported to the Pi.
Also, there are also some nice Pi-specific pointers in this thread: "Setting up SHT11 Humidity and Temperature Sensor" viewtopic.php?f=37&t=38506