What percentage of dollars are you paying over the FMV the hard assets less any debt still owed on those assets?
That is what you are paying for (intangible goodwill). That is the true cost of buying the business rather than starting your own from scratch. And that is what you are risking when considering future obstacles. This owns you are not doing some sort of buyout over time (3-5 years).
The heart of any construction business is knowing your costs. The value of the business is the owners knowledge of that. How are you acquiring that?