Hey dumbass!
For the compressed version of the game you'd want around 6GB and for the hi-res version you're looking at 15GB.
If your hardware supports the VP8 codec that's a bonus, but if your system was made within the last 10 years, you should be good to go.
Both the compressed and hi-res versions of the game are rendered in 1080p. Compressed has a lower quality in regards to images and videos, but if you're playing on a smaller screen, you might not notice a huge difference.
Hope that answers your question!