Can you break down the costs of a new build?

You are right to break the build up into six to seven stages. However, I would tend to put ground and second floors together into one stage, and to add an extra stage at the end to cover finishes and externals. Also, from a costing point of view, it’s not helpful to split electrics, plumbing and carpentry into first and second fix.

In reality, there is no ‘industry standard’ for breaking down build costs, but you won’t go far wrong if you work to a break down such as the following:

Groundworks and drainage: typically 15% (though it can be significantly more on difficult sites)
The shell, up to wallplate level: 30%
The roof structure and cover: 12-15%
Plumbing, heating and electrics: 12-15%
Plastering, wall finishes: 8-10%
Finishes (kitchens, floor covers, stairs, joinery plus externals): 20-25%

These proportions tend to keep in balance whatever the build size or quality. If you elect to build in timber frame or one of the other factory-built systems, you would place the supplied superstructure into a separate stage.