@CFL7
Not only is it not the right way to do clean bookkeeping, it's not the right way to do bookkeeping at all.
Having said that, here is how it's done. Let's say the LLC is Co. L and his construction business is Co. C. When Co. C pays for the expenses of Co. L, you will need to correctly book the expenses in Co. L and record a corresponding liability called 'Due to Co. C', since Co. L needs to reimburse Co. C for the expenses it paid on its behalf. You will need to create a journal entry in Co. L to do this: debit the expense, credit the 'Due to Co. C' liability account. Then, when you reimburse Co. C, issue the payment and assign the 'Due to Co. C' liability account to the payment. That will keep the expenses in Co. L, but instead of paying the vendors/contractors, you are paying Co. C.
In Co. C, when the payment is made for Co. L's expenses, instead of assigning an expense account to the bill/payment, you will assign a 'Due from Co. L' asset account to it. Then, when you receive reimbursement from Co. L, assign that same account to the deposit. That will keep all of Co. L's expenses off of Co. C's books.
Bottom line is to make sure you keep the income and expenses in the proper company. If you're asked to book income or expenses in the wrong company, that crosses the line ethically and possibly legally as well.
