Requirement for visa to purchase items for my building project.

Since you want to go to purchase something in China, you need to apply for a M type for going there.
Then you need to prepare an introduction letter from your employer, an invitation letter from your partner in China, photocopy of registration paper, tax clearance certificate, bank statement for at least 4 monthes' history, round trip flight tickets and hotel booking confirmations, your valid passport and application form with recent taken photos to apply through your local Chinese embassy.