Here is how the California Board of Equalization classifies what labor is subject to sales tax:
Retail sales of tangible personal property in California are generally subject to sales tax. Examples of tangible personal property include such items as furniture, giftware, toys, antiques, clothing, and so forth. In addition, some service and labor costs are subject to sales tax if they result in the creation of tangible personal property. Based on that qualification, it does not appear that your labor will result in the creation of tangible personal property, and therefore would not be subject to sales tax.
I am giving you a link below to the section of the California BOE that addresses this issue.
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