In brief
The brick Gothic building collects later chapels and historical periods.
Useful to know
The cathedral in Roskilde was built in the 12th-XIII century of brick and is important for the spread of brick Gothic in Northern Europe. For centuries, side chapels and anterooms were added to it. [1]
In a plan, distinguish the main body from the supplements. They are not just a deviation from the original symmetry, but a testimony of continued use. Then compare material unity with style differences. A common brick environment can collect parts from different centuries without building history fitting into a single date.
Sources
For further detail and to check the information: