If you are coming to Berlin, plan ahead and book a tour at the Reichstag. Being a government building you can't just walk up, as appealing as it may be, and expect to be ushered in. We booked a few weeks in advance and had no problem getting a booking. Alen, who I went with did the booking, and got us on an English tour which was well worth it I thought. The other option is to just get a booking to go to the observation floor and the dome. We actually got to see most of the building and also the assembly hall while learning some interesting facts.