I do a bit of both. Have tea and coffee available , and I put out mugs etc and say that they can help themselves, so long as they wash up and leave it tidy. I also offer that they may sit in comfort to have their lunch, use what plates they want, so they can get fish and chips or whatever they bring and sit in the warm at the table and not have to sit out in the cold.
When I had people in actually sorting out the whole kitchen I chose to make some ginger parkin , which I left for them to help themselves to. My idea is do as you would be done by, and have always found workmen never take advantage of me and have washed up after themselves and left everywhere tidy, and have been grateful for the parkin.
My brother once years ago, spent nearly a whole day working in this womans house and she never even offered him a cup of tea, whilst making several for herself. He had his own stuff of course but personally I could not have had someone in my house and never even offered them a drink. Maybe I have been fortunate, but I have never had anyone take advantage of what I offered, and even , as one young man saw how difficult it was for me to move about, not only swept up all round where they had been working, but asked for the hoover and even hoovered my lounge for me, which they had not even been in, but saw how difficult it was for me. So we do what we feel comfortable with, but on a day like today, which has been really freezing cold, I would have invited anyone working at my house to eat inside .