Deborah,
Right attitude, there's not a lot of difference between the two, our girls and lads who do office cleaning also double up on builders cleans as well as domestic cleans and end of tenancy.
At the end of the day it's cleaning, not rocket science! If you have confidence in what you do now you should have no problem in giving a satisfactory service to commercial and builders.
Ask them what they want and deliver on it.
I have a standard specification for build cleans of what cleaning is involved, send me your email and I'll return a copy to you.
Ian