作る and 造る: making food and building a ship
Compare spellings of つくる through food, sentences, ships, and brewing, without choosing solely by an object's size.
Make food or compose a sentence
家族のために夕食を作りました。 says that someone made dinner for the family. 作る, read つくる, broadly covers everyday creation, including food.
習った言葉で文を作ってください。 asks someone to make sentences with the words learned. 作る applies to sentences or plans as well as physical objects.
Building and brewing
この工場では船を造っています。 says that ships are built at this factory. 造る, read つくる, is used for constructing things such as ships.
この蔵では米から酒を造ります。 says that this brewery makes sake from rice. 造る also applies to brewing, so it is not restricted to large objects.
Look at the combination and use, not just size
大きなケーキを作りました。 says that someone made a large cake. Size does not automatically require 造る; consider the food-related combination.
The uses of 作る and 造る overlap. Learn combinations such as 料理を作る, 船を造る, and 酒を造る without turning the spelling distinction into an absolute rule about every method of making.
Must 造る be used because the cake is 大きなケーキ?
Show the answer and why
No. 大きなケーキを作る is appropriate. Choose by the object and its usual combination rather than size alone.