I typically use Means to get an idea, use the OH&P numbers for extra fluff, and then add a 10-25% contingency - depending on the client, the scope, and complexity. My numbers are typically higher than the bids but clients do not mind paying less.
As stated in another thread - there are skills that can help an engineer in his job that are not specifically structural engineering.
Estimating is one of these skills. I have had bids come in higher and lower. The thing I try to stress to the client is that I can provide an estimate, but a competitive bid will give you the going rate for the work to be done.
One thing to keep in mind in using means is that there are alot of "rules". It breaks things down to the part, but also gives some rough overall pricing. A person needs to make sure the numbers they are using includes everything. I would also verify some of the overall rough numbers with contractors to give yourself a better feel for where the numbers should be.
Maybe this is a stupid question, but did you use the location factors in the back of the book? If you just used the raw prices and didn't adjust them for your location you could be way off, especially in the northeast or California. Also important is inflation for large projects and compressed schedule.
Means has difficulty capturing very localize phenomenon. For example, in my town, for a couple of years, masons and masonry contractors were in very short supply. They had more work than they could handle, and as a result, were able to charge prices far, far above what MS Means would show for masonry installation. If you did any estimating involving masonry, you had to adjust for the local market conditions which were at least twice what RS Means had.
The best source for such information is local general contractors who might owe you a favor or two.
There are many things that can affect costs. As an engineer, you need to develop your skill at understanding and applying adjustments as needed to the Means numbers.
Just a list of a few things that I can think of:
Bid environment
Winter construction (temporary heat and protection)
Size and quanity of various operations
Site access
Site with direct crane and material access or inside a factory a long way from a loading dock.
Special Owner's requirements
Degree of difficulty (for instance: erecting steel over an operating machinery inside an existing factory or bringing steel up an elevator and erecting it inside an existing hospital.
These conditions can dramatically affect the cost and Means is generally set up only for new buildings on a Greenfield site.
In Australia, a separate profession, Quantity Surveyors, who are professional estimators, do the prebid estimates for buildings. Structural engineers and architects exclude this from their work. The building services are usually still estimated by the engineers.
