The only way I know to build working capital is to spend less than you take in as income and save or invest in liquid assets the difference. Working capital is liquidity you have ready access to that can be used for operating expenses.

Once it is spent into something that is illiquid, it is no longer working capital but a prepaid expense or a longer term asset.

My opinion. I'n not an accountant but that is the way I look at working capital.

John