Know when the money leaves, month by month

A budget tells you whether you can afford the build; a cashflow tells you whether you can afford March. The same total spends very differently depending on when the big bills land - the frame, the roof, the glazing, the kitchen - and self builds run into trouble not only by costing too much but by needing money faster than it can be released, especially where funds arrive in stages. Before anything is signed, lay the spend out month by month against where the money actually comes from, and move the collision points while they are still on paper. The free Cashflow Forecast template does exactly this.