I frustrated about the space between levels for a while; did my research. There are a ton of folks that have two levels and by looking at their bench and track plans I sorta got an idea of what would work for me and also things that I didn't like. I have also operated on multi-level layouts; one huge one ( 4000 ft ) and some smaller [normal] room size ones. The big one was 30" between levels and you followed your train around. Took about 35 minutes to make a complete loop of both levels without any switching operations! The smaller ones were 18 to 24 inches between and were more inclined to switching than long main line runs. Once I got the hang of them it was fun. I found that the 18 inch distance was sometimes a pain as you would have to bend down slightly to see your train if the main went close to the back of the lower level. One had 'reach in' problems and they padded the ...um.... ceiling of the 1st level so you wouldn't get scars coming out. Took about three times and you learned NOT to stand up directly, but to back out first.
If you intend to use a helix, try to figure out how to make it a start/stop point as waiting for trains to traverse it is boring. Think about it, assuming a 24 inch rise and probably 4 inches between helix levels and a given of a 2% grade, you are looking at about 100 feet of track that goes nowhere except up or down. I would think that a 3% grade in a helix would be pushing it considering the curve radius. Train length might be a problem and you could end up with the middle of the train in the helix hole and on the floor.
A room-lix ( around the room grade ) could be considered yet another level. Now you have trains at the back of your benchwork that operators can follow and if done proper they won't have to bend down to see them. I suppose that you could bring portions of the grade out to the front for a industry or scenic rendition, but that ends up using space on your lower plan. Could be great for scene division.
Given the above and the research that I have done, I have decided on how to approach this problem: I have 24 inches between levels, 6 helix loops of less than 2% which makes my radius 30 inches. Should be able to stop and start a train on the grade without problems. My helix is also going to be used for serial staging as it is 5 tracks wide; 2 inside for down staging, 2 outside for up; middle for continous running. My train lengths are set a 15 1/2 feet max, so I should be able to stage 24 trains ( 12 up, 12 down ). Note that the outside radius is 38 inches which makes the helix footprint 6 feet 10 inches in diameter ( 2 inches on the outside for clearance ). I am setting the upper and lower entry points as 'crew change' locations where an operator can quit the current train and get another headed in a direction of choice. Given your room size something like this would have to be shoe-horned in as it would take a big chunk of real estate.
I have enough room to also include another way up/down and is considered my 'mountainous region'. So say an operator starts at the crew change point and heads away from the helix. The operator can follow the train along the lower level, through the mountainous area to the upper level and back to the upper crew change location. Scary isn't it? In your case with a 8x11 room, and we assume that you have no doors or windows, a one loop room-lix would be 38 feet which works out to be about 3.9% if you have 18 inches of seperation. If you can figure out how to do two loops, your grade would be less than 2% and better for operation. Don't know if that will work for you or not.
You didn't state your scale and I assumed HO. If you are an 'n-scaler' that changes stuff a bunch, Your helix would have a smaller foot print and could be doable in your room. Grade is grade no matter what scale you model and you still need at least 18 inches for level seperation.
It all depends on what YOU want to do. If you are bent on a 3% grade single track helix, build that first so you can test your train lengths vs the helix because if you have problems after all is done, that will be no good.
Todd Hackett Chief Hogger and BottleWasher
Libby, Montana 59923
railpix - http://www.soundrail.com
I take only pictures then leave footprints on railroad property that I know is not mine, although I treat it as such...