It's actually a fairly straightforward project, especially if you've setup a Raspberry Pi before (or eight #fromthevault)! Basically you're just installing an application, and setting up a microphone and speaker. Nothing fancy.
There are already some great guides for getting started too for both Raspberry Pi and Alexa. I'm just going to direct you to these, give a rough overview, and add some additional tips.
Here it is in action:
For equipment, you'll need:
1. A Raspberry Pi 3 with SD card and USB micro power source:
- Raspberry Pi 3 Model B
- USB Micro Charger
- High Speed 16GB SD card (8GB Works but 16GB leaves room to play)