Class A's are built on a specially-constructed chassis designed for motorhomes. Lengths range from 26 - 45 feet. Slideouts are common. Pushing a button makes part of the room slide out, and voila!, you have more space.
Newer models have as many as 4 slides. The "home" part of the motorhome includes its own heating, air conditioning, electric system, propane supply, and water tanks (fresh water, grey water, black water).
Accommodations include all the essentials - kitchen with microwave/oven, fridge, cooktop, dining area, living area, bedroom and bathroom. Washer/dryer may be standard or an option (or you can use the space otherwise - based on your lifestyle). It's pretty standard to have a VCR and two TVs (living and bedroom). Flat screen LCD TVs are becoming common at the high end of the spectrum.
The further you go up in price, the more bells and whistles - hydraulic leveling systems, electric awnings, heated ceramic tile floors, dishwashers, trash compactors, automatic sunscreens, GPS, and so on.
At the most luxurious end of the range, Class A motorcoaches are called highliners. And at the top of the heap, and some would argue in a class by themselves, are totally custom coaches like the Prevost. Suffice it to say that there is a wide array of choices, floor plans, and interiors ranging from practical to luxurious - with corresponding price tags from $60,000 to over $600,000 to the millions of dollars.