A service contractor's books work when they can answer two questions: which kind of work makes money, and what the vans really cost.
Revenue, split by kind of work
Service revenue — repairs and call-outs. Installation revenue — replacements and new systems. Project revenue — larger, multi-visit work. Maintenance agreement revenue — recurring plans.
These have genuinely different margins and different cash timing, so a single revenue line hides which part of the business is carrying the rest. See revenue categories.
Maintenance agreements deserve their own line even when small, because recurring revenue is worth several times the same amount of one-off work and should never be buried.
Direct costs
Materials and parts, subcontractors, direct labour, equipment hired for a job, and permits pulled for a job.
Permits and disposal fees are the two most often absorbed rather than billed, and both are genuinely job costs — see cost of goods sold.
Vehicles as their own group
Fuel, repairs and maintenance, insurance, lease or finance payments, and tools.
Grouping them together is what makes the fleet's true cost visible, and in a mobile trade it is usually the largest cost after people — see vehicle costs.
Compliance as its own group
General liability, workers compensation, professional liability, licences, permits and bonding.
Contractors carry more of these than most businesses and they are largely fixed, so they belong together where they can be reviewed against renewal dates rather than scattered through general expenses.
What this setup gives you
Margin by work type, the real cost of the fleet, and a compliance list with dates on it. Those three answer most of what a contractor needs from their books.