There is a MRY custom cake shop on the 0/8th floor of City Square/KLOC-where there are DIY cakes, but the variety is relatively small and expensive. Another disadvantage is that the elevator on the 18 floor has to wait for a long time, and it is not very convenient to get in and out with other people.
There is also Xinyi DIY Workshop near Xintiandi, Guo Mao, which specializes in DIY baking and is located in the second phase of Wanzhou Garden. It's hard to find, but it's big, with two floors and parking spaces. Not only making cakes, but also cookies and puffs, as well as cupcakes and pizza, which is more cost-effective. The boss is nice and often teaches baking knowledge.