I don't do floors but your question can be extended to just about anything. In my experience, it's a bad idea to have customers do any of the material ordering. You're just opening yourself up to a lot of potential problems. What happens if there isn't enough of/the correct amount of material - is the customer going to drop everything, leave their office and drive to pick up what you need? Are they going to reimburse you for your time while you sit around waiting for them to get what you need? What happens when the materials aren't there when the customer said they would be? Will they reimburse you for the time you lost waiting for it to arrive.
In my experience, is that if they want to start off by controlling things by ordering the materials, then there is a very high probability that they are going to be a big PITA during the job and long after you've finished even.
The bottom line is that you have to decide for yourself if you want to have the customer provide the materials and take the chance that everything will still work out.
Good luck!