Do just what a good GC would do on a very custom job:
1. Break the project into known and unknown scopes.
a. Known – for example 42 electrical outlets at $75 each, 5 doors at $200 each. These are items that you can see and there isn’t any reason to believe that these costs may vary. If you are uncomfortable doing electrical work or plumbing work these may be subcontracts that you get fixed bids on. Again the point is NO CHANGE in the future.
b. Unknown – these are tasks that may change in scope. For example, you are too lazy to pick out a light fixture, tile or plumbing fixtures now, or you want to make the choices later. Establish an allowance budget for these items now. Be realistic but don’t sweat the details.
2. Confirm (price) the known scope – this can be accomplished by going to the store with a shopping list and pricing it or asking subcontractors to give you prices on their specific trades.
3. Make allowances for the unknown scope - if you have to remove a wall it is very easy to estimate how long it will take to remove and replace the GWB. It may not be easy to estimate how long it will take to repair the rot behind the wall but don’t give up on the whole process as being too hard to estimate. To repeat; estimate the knowns (fixed priced) and document them. Make a guess at what you can’t see. It really burns me when subcontractors try and tell me that because it is a remodel they will only work on a T&M basis. Do you mean to tell me that a plumber doesn’t know how long it takes to rough in and set a sink or toilet? OKI believe that those costs are known and it is the vast majority of their work. When you pulled the wall apart, it turns out that he has to run 16’ more copper to get around a column or spend a few more minutes notching a beam for the toilet. OK, those are unknown, but how much did they cost? What we’ve done is control the risk. We’ve isolated the allowances and they are a very small part of the project.
4. Give yourself a contingency; the size depends on the size of the project. Start out at 25%. Do your estimate and revise your scope (eliminate or add back things you need or don’t need) if you want to. Revise the estimate and only use a 20% contingency. Make some more decisions and get subcontractor quotes. Do you feel comfortable going down to a 15% contingency? Remember, no matter how detailed your estimate is, something will change and you will need (or want) a little more money than the “bid.”
5. Use your estimate as a sounding board. If a subcontractor says they need more money, get really specific: what is actually different than was estimated. The more detailed the original estimate from the contractor, the easier this step is. If it looks sketchy to begin with, the little red flag goes up. If you over spent on plumbing fixtures, under spend on electrical fixtures….. You will find that the allowance budgets are far smaller that the known (fixed) budgets. If you watch the allowances closely you won’t go over budget.
6. If you live with a mate, tell them you love them on a daily basis, even if you are tired. If you live alone, include a friend for support.