Answer:
Buying a shirt contributes both in the production side of GDP, and in the consumption side of GDP.
Step-by-step explanation:
In the production side, the shirt becomes part of GDP when it is sold, and only its final value is accounted for, because intermediate costs like the costs of raw materials are not included since otherwise we would be making double accounting. The final value of the shirt becomes the producer's income.
In the consumption side, the consumer contributes to GDP for the amount of the final value of the shirt. The final value of the shirt becomes then, the amount of money spent by the consumer.