My wife and I have ridden the Builder a half dozen times over the past decade, all being in the fall. The first trip was in coach. While the seating is quite comfortable with good legroom and reclining backs, you do get some kinks from not lying out flat. Best seats for coach riding are two-thirds back from the front of the car. The very end seats are noisy from people going through the vestibules. The middle seats have people going up and down the staircase where the lights are on all night.
The roomettes are cramped, but private. Whoever gets the top bunk needs to be a bit of a contortionist. Once in place, the bed comfort is pretty decent. During the day, we would leave the door open for better air circulation if the roomette was on the sunny side of the train. Take along some safety pins for the curtains! They open and close horizontally so if you want to cut down some of the sun glare, you can use the pins to pin the curtains upward vertically. That way you can still see the whole panorama.
In the middle of the night, the train splits at Spokane where the rear half and lounge car becomes the Portland section while the front half and diner continue to Seattle. The Seattle section gets to ride through the Cascade tunnel while the Portland section gets the Columbia River Gorge views.
As Eddie said, the diner food was quite decent. If you get the roomette, your meals are included. You won't go hungry! Going coach, the lounge car has food service from 6AM to 10PM or so. The fare is the standard box lunch stuff; bagels, salads, hot dogs, hamburgers, etc., plus soft drinks, wine, beer, and coffee.
The scenery is gorgeous. Urban Chicago and Milwaukee changes to the north woods of Wisconsin. From Minneapolis the scenery goes flat through the Detroit Lakes. That stretch is usually done after dark. It is (or was) a stretch of jointed rail so the speed limit is lower and the ride is pretty rocky. If you are in the upper bunk, you will be glad you have the netting to keep you in place!
On towards Minot, there are vast farmlands. Havre is a crew change spot where you can get off for a while to stretch your legs. West of Cut Bank and into East Glacier, the scenery becomes mountainous. When we travelled in the fall, it would be nearly dark then.
A few observances: In the summer, there will be children riding in the coaches - not all parents are attentive. There will be a number of smokers who will be standing by the doors when the train makes some of the longer station stops. Not everyone knows how to flush a toilet! I still think there is a contest between North Dakota and Montana to see who can stack the most scrap metal in their back yard! 
I would advocate anyone to take the trip if they can. It's an adventure!
Neil
