Describe the finished result
Write down what the project must do and the dimensions or capacity needed. In the UK or Ireland, a comparison between suppliers is meaningful only when the specification is the same. Separate essential parts from optional additions before collecting prices.
Include the less visible costs
Add delivery, fixings, preparation, storage and the tools you actually need. Include replacement or maintenance items where predictable. Record your own time separately so a project that is enjoyable but time-consuming is not presented as an effortless financial saving.
Use current local quotations
Keep the date and scope of each price. A price from a different region or an old article may exclude transport or describe another material. Compare reuse options on usable condition and preparation, not just the purchase price.
Review after completion
Record actual spending and any materials left over. Compare the finished project with its original purpose rather than inventing a return from every potential future use. Start the next project with what you learned. A realistic small budget is more useful than an impressive saving based on quantities the household never needed.