how much space does it take to download killing floor 2

Borderlands says "8 GB or more" on steam.

Metro 2033 Redux - 10gb
Metro Last Light Redux - 10gb
S.T.A.L.K.E.R.: Call of Pripyat - 6gb
S.T.A.L.K.E.R.: Clear Sky - 10gb
S.T.A.L.K.E.R.: Shadow of Chernobyl - 10gb
Fallout 3 - 7gb
Fallout New Vegas - 10gb
Crysis 2 - 9gb
Far Cry 3 - Blood Dragon - 3gb
DayZ - 10gb
Insurgency - 10gb
Paladins - 10gb
Brink - 8gb
F.E.A.R. 3 - 10gb
Call of Juarez Gunslinger - 5gb
Call of Juarez: Bound in Blood - 4gb
Singularity - 9gb
Medal of Honor: Airborne - 9gb
Spec Ops: The Line - 10gb
Dead Space - 7.5 gb
Dead Space 2 - 10gb
Condemned: Criminal Origins - 8gb
The Darkness II - 10gb
Sniper Elite: Nazi Zombie Army - 5gb
Sniper Elite: Nazi Zombie Army 2 - 6gb
Sniper Elite V2 - 10gb
Splinter Cell Conviction - 10gb

And there are many more but I don't have time to list more right now.