Your job cost will be Direct cost plus the overhead.
Direct cost will be-
Materials used for the job
Labor cost (including payroll tax and wcomp liab) for the job
Other expenses such as permits or other costs directly related to that particular job.
Overheads will be-
the office rent, if any
the equipment rental ( if the same equipment is used for various jobs)
office administrator salary
Any other expenses you incur in business(not included in direct costs above)
A percentage of the overhead cost needs to be added to the direct cost as calculated above in order to determine your total cost for the job.
In order to arrive at the overhead cost rate- you can determine overhead rate based on the prior month total overhead cost divided by the direct cost. And for this job you can allocate the overhead based on the percentage so calculated on the direct cost incurred for the job.
This will give you the total costs incurred for the job.
You can have a P&L for each job if you want to evaluate each job separately.
Let me know if you have any question.
Please note: This advice is provided with the understanding that all the relevant facts have been provided by you. Any change in facts might affect the advice given and hence may not be relied on in such cases. Nothing contained in this reply was intended or written to be used, can be used by any taxpayer, or may be relied upon or used by any taxpayer for the purposes of avoiding penalties that may be imposed on the taxpayer under the Internal Revenue Code of 1986, as amended.