I am sorry but Big ben is just a simple tower without any architecture bonus... there is a lot of towers around the world, this tower is just well known, but not very interesting building. If tower, then Pisa tower. But again, the most important factor is that TLG already made a set from London. I cannot imagine to make another London landmark, while there is a lot of much better and interesting landmarks from other parts of the world. If making another set from same country, then USA - much much stronger market than UK. If TLG makes new landmark every year, OK, we can see landmarks from same country, but not in this situation, when TLG has made just 5 landmarks during 16 years. Here is my list of most interesting buildings + reason why are better than Big Ben: Pyramids - 1 of classic 7 wonders and maybe most famous building from the earth. Of course, it is a simply building, but adding the Sphinx would be solve this problem. As an alternative can be Chichen Itza (but this would be better as an Architecture set). Colosseum in Rome - there is a big hole in TLG production - ancient antique - and this set can cover it. As an alternative can be Athens temple. Neuschwanstein castle - German is a strong market, so a german landmark makes sense + this fairytail castle could be easy one of the best lego sets ever. As a simplier alternative could be Brandenburg Gate. St. Basil cathedral from Moscow - again, this colorful and interesting building could be wonderful set. Burj al Arab from Dubai / Petronas towers from Kuala lumpur or other modern buildings, which looks great.