a weird answer for a weird question: actually you can check epiwar has 9734 index pages for 25 results on each page. you know that maximun multiplayer map size is 8mb. if you check campaign maps, you get 14 pages per year then there's an innacurate amount of 3500 campaign maps that could exceed max map size.
doing maths:
9739 pages * 25 maps = 243475 maps * 4 mb (average) = 973900 mb
9739 pages * 25 maps = 243475 maps * 8 mb (max mp) = 1947800 mb
giving an average amount of 50mb to campaign map it equals to = 175 gb
that means 2.2 TB.
aprox 55 hours at 100mb /10 mb download.
if you spend 10 secs per each map click then you will need 675 hours extra
that means 30 days without stopping.
of course it's not accurate. it's a stupid calc @_o