Just to be clear, if you're a VAT-registered tradie doing a job for yourself, you are obligated to pay VAT for the materials. Diverting vat-reclaimed materials for self-supply is tax evasion (which can be identified by auditing invoices). So legally speaking, the only money saved is the VAT on your own work hours.
Slightly ironically, self-supply is much easier and almost impossible to identify when devs use work-paid subscription services (e.g. Claude Max) on personal side hustles.