Hello,
I'm in my early 20's and currently employed as a rail Sparkie. I have had about 6 years in the construction industry on generally the industrial/ commercial side of an electrician. I have worked on rails, tunnels, hospitals and high end apartments. Made this AMA because I was bored and generally wanted to know what the public think of the trades .Ask me anything and I will do my best to answer.
Hard to say, as if you dont have background knowledge, you dont know what to look out for. If there a minor variations here and there and are not hard to adjust, I wouldnt bother charging them. If there are multiple problematic variations that require constant rework and attention, you need to start charging for variations. If you give them an inch, they will take a mile.
Generally the client supplies all materials and gear, if there are add ons or variations to a plan, they create a seperate quote and charge the client for everything (Labour, materials, call out fee, machine hire, permits, admin, etc). Either that or they use a proprietary material/ equipment that is only distributed by themselves and put a insane margin/ markup on.