I personally don't believe in ramps that much except for chickens that can't fly, like Silkies, or in special cases. Ramps are a tool that have their place. Many people would be surprised at how well a two-week-old chick can fly, especially when they are motivated. There is a reason wing...
Great, I love the flexibility.
If the floor is elevated you can put a wire floor in one or more of those sections and have a broody buster as well as for medical/behavioral reasons. My permanent 3' x 6' brooder has 1/2" hardware floor and is up off of the coop floor. The poop falls through...
They give the internal dimensions of the brooder, the part where the chicks are, as L 35.8” x W 19.3” x H 15”. I would not try to keep 20 chicks in this until they are five weeks old. Their capacity chart shown below agrees.
I know this is getting a bit picky, but that "week" chart is a bit...
Are you looking at a specific brooder to buy? There are many different ones out there, it's easier to evaluate if we know what you are looking at.
What are the temperatures inside that garage/work shop? How stable are they? To me the biggest challenge in brooding outside are the temperature...