There was looong line of visitors to the Reichstag on Sunday afternoon (western facade). I didn't have enough time (approx. 1 hour) to wait there although I wanted to to get to its dome which was open to the public.
I suppose that the line is shorter just after opening at 8.00 am and on business days. On the other hand it may be longer in summer season.
Just remember to take some Euro coins with you when you travel, especially by train, as the restrooms usually require 50 Euro Cents to 1 Euro. When you've been sampling all the Beer, sometimes it is just too long a wait to find change!
Should you wanna get up the TV tower Fehrnsentrum, never try to climb up manually without any guard or safety stuff. Even when youre born to be an crazy adventurer, consider to get help from other and pay your life insurance first. :))
Otherwise, just get up by normal way inside. Nothing to loose to pay some euro, better than have to take a bigger risk, dont ya think?