I don't know of any resources or references, but I have seen and used a variety of contingency percentages (usually anywhere from 5% to 20%).
I really think that it is up to the estimator to decide what contingency percentage he wants to use. On a project that you have designed and thought out down to every last bolt...then you would want to use a low contingency percentage(5%). If you aren't real familiar with the project and the work involved, then you would want to use a high contingency percentage (20%).
From my past experience, I'd say go high...unless you are trying to win a bid, and then I'd suggest you design it out to every last bolt and use a low contingency.
I hope this helps. There are a number of estimating books out there, and I looked in one of mine for contingency numbers but didn't find anything. Good luck.
I would say that the most popular estimating handbooks are the Means books. These are pretty good books, and there is a book for just about everything. I have a couple that I use from time to time.
If you go to Amazon.com and do a search for Means Estimating, you will get a long list of books. There should be a book for what you're looking for.
The cost of engineering ranges from 3- 20% as noted. IT Varys with the complexity of the project. K-marts are a very low percentage , Lasor fusion plant very high.
If you'r involved in construction and engineering to any extent you should subscribe to ENR (Engineering News Record sorry this is not intended to be a commerical plug for them. They are published by Mcgraw hill and are on the web at enr.com). They publish quartly cost data and general articals on construction.
One very good rule to remember is "Nothing is as cheap as good engineering" and it corallary " Nothing cost as much as poor engineering" When your project is falling behind schedule and your contractors are overwhelming you with change orders that bargin low bid engineering package you got won't look so good. Money spent wisely up front pays o big dividens later.
The design-build approach with a good engineer contractor team can cost more but be cheaper in the long run. Concurrent engineering/construction can save months on a schedule. If your product is valuable enough a month of extra production will pay for the best engineering you can find.
Percentages vary according to the project requirements and competitive business climate. For example a typical petrochemical facility would be on the order of 18% of the capital cost ( or Total Direct Cost), this would translate into 12% of the bottom line (Direct plus Indirect).
Don't forget that in addition to the cost items you noted - I would call them Home Office Engineering and Construction Management respectively - you'll also have Sales Tax, Freight, Contingency, (perhaps) Owners Costs, Fee, and Contractors General Liability Insurance (CGL). This is only a partial list.
a good book for cost estimating is by Peters and Timmerhaus "Plant Design and Economics for Chemical Engineers", R.K. Sinnot "Coulson and Richardson Vol. 6 Design" and by J.M. Douglas "Conceptual Process Design"
