So you want to record temperature measurements over time?
I have used the Adafruit guides to teach myself how to log the weather. They're fairly easy to follow and the guides are updated regularly.
See this Adafruit guide on how to publish temperature and humidity readings to Google docs - https://learn.adafruit.com/dht-humidity-sensing-on-raspberry-pi-with-gdocs-logging
The Adafruit guide uses a DHT11 sensor that can measure temperature and humidity. My advice is to use the slightly more expensive DHT22 sensor as it's more accurate, has higher and lower humidity sensing, and is more stable.
You can add multiple DHT sensors to a Pi but each sensor requires one dedicated pin on the pi (26 pins are usable of the 40 available). You can also use DS18B20 1-Wire Temperature sensors to record the temperature. These can be "networked" together requiring just one pin on the Pi.
Adafruit guide on DS18B20 temperature sensors - https://learn.adafruit.com/adafruits-raspberry-pi-lesson-11-ds18b20-temperature-sensing
You might wish to record the ar pressure. Adafruit again has a guide but it looks out of date - https://learn.adafruit.com/using-the-bmp085-with-raspberry-pi/using-the-adafruit-bmp085-python-library?view=all
I have 2 Raspberry Pi's running 24 x 7 x 365 days a year measuring the weather. The data is dumped to a MySQL database running on a website.
Pi 1 (at rear of property) - 2 DHT22 sensors (one inside, one outside), 20 DS18B20 temperature sensors, 2 Light sensors (inside and out), pressure sensor, Pi camera
Pi 2 (at front of property) - 2 DHT22 sensors (one inside, one outside), 5 DS18B20 temperature sensors, 2 Light sensors (inside and out), rain sensor, wind sensor, pressure sensor
Raspberry pi 3 chosen as it has built in wifi and low energy Bluetooth. Cheaper older models are available but you'll have to buy Wifi adapter. Most guides are written for Pi 3. This would run on a Pi Zero (£5) but you then have extra problems with things like 1 usb port, soldering on the headers etc.
You can run a Raspberry Pi 3 from a normal USB power supply (mobile phone charger) as long as it can supply at least 2 amps. The Pi will run on power adapters supplying less than 2 amps but you may run in to problems.
Sometimes you can buy higher capacity memory cards cheaper. You need at least a 4gb memory card and I currently use 8gb cards. I backup my cards every time I make a major change, so backing up 16gb card's would require more space. The Pi supports up to 64gb micro SD cards.
Equipment Required (total about £60)