What should be in the plumber's proposal to add a 1/2 bath off my kitchen. How do I know if anything is left out of the proposal?

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I have been given a proposal for plumbing work for adding a half bathroom off my kitchen. What should I expext to see as a check list in the proposal for work to be accomplished

First off, I'd get 3 bids not just one. Make sure everything you want is listed and nothing you do not recognize. Is this a rough in bid only or finished bath with toilet and sink?

This is a rough bid. The new space is an existing empty closet about 10ft away from the main waste, vent and water pipes... located on the first floor of a 3 story house. One full bath on the second floor and 1 half bath in the basement. Bathroom fixtures will only be sink and toilet. Space size is quite small, but adequate to accommodate a tiny corner sink and a 25" toilet. What should my check list be in evaluating the plumbing proposal?

Buy the sink first and make the plumber plumbs his rough drain to meet the requirements of the sink. You should have a hot and cold supply to the sink with shut off valves just inside the room, same for the cold supply to the toilet. Also determine what you want to do for the flooring and have the plumber set the toilet flange flush with what will be the top surface of the floor. There should be a permit pulled , likely by you but the plumber must pass a city inspection, be licensed and insured. He must submit a drawing of his piping, materials to be used how he is going to vent the fixtures.

A half bath isn't nearly as complex as a full bath.
I'd pick out the toilet, sink, flooring, wall covering, mirror/med cabinet, light fixture, faucet. If you leave all those open, you may get 'contractor' bottom of the line ones. Better to buy them yourself. If you don't care, fine.

You want work done to code (GFI outlet, low flow toilet maybe). The plumbing - pretty standard.
I'd specifiy a range of days for the start date, after all the fixtures are on site, so that work proceeds in a timely manner, and a penalty if he's late.
Drop cloths on the kitchen floor and to the door outside.
Full debris removal.
Guarantee.
Copies of invoices for fixtures if he buys them.
Never pay for the whole job in advance, but have a check ready for the balance when he is done.