Sweep/loft command in any 3D software?

I am pretty sure I have sketchup plugins that do this in 10 seconds.

or wait... are you trying to build a physical model? If so, cudos.

I've built similar models many years ago. I cut identical width strips of veneer wood and curved them along the inside of a large cylinder where I had marked the heights. Pin the thin wood in place with weights and whatnot and repeat for the other side. You fill in the ramp part afterwards with a large sheet and sand it to fit.

Thanks for the quick reply. Unfortunately it's a physical model - it's not too late to change it to a hexagon or something much much easier.

I'm making it with mountboard so no sanding can really be done. It wouldn't be accurate but do you think if i made the edges first (excluding the top surface) and literally traced over where to cut the top surfaceusing tracing paper and transferred that shape onto mountboard it would work OK? It's very awkward altogether..

My teacher is aware of the difficulty and didn't seem to fussed if it isn't perfect (and probably has no idea how to help)

Throw it into a program that has the unfold command (Rhino, FormZ, maybe there's a sketchup plugin?) - which will essentially flatten out the model.
 

I'll give that a go now - we haven't started CAD yet (i know, i'm a baby). I've used solidworks before so hopefully I can figure it out. Thanks

You will need to use a laminate procedure mentioned above or splice two arks that are slightly more than half the diameter of the circle to account for the vertical rise over run. 

Solve the length of the inside and outside edge it is essentially a big triangle warped around a tube, use a tube of paper that will be the diameter of the inside an outside of the ramps, cut the paper to match the slope of the ramp you need plot the length of the line on a sheet of paper

the inner arch or the ramp edge when plotted on a flat paper will have a larger radius than the plan view because it wraps around as it slopes. then in some drafting software offset the width of the ramp and plot it out  on paper first and then cut your expensive model materials once you have the radius and the length figured out. I would print out the ramp first on cheap paper and see if it fits before cutting up something expensive. This may take a few tries to get ti right

Peter - that sounds like the simplest way. For the 'triangles wraped around a tube) do you think i could make a right angled triangle which is 9m (approx arc length) on the adjacent and 1m opposite (how much i need to rise) and that would be used as the edge? would that gradient work out okay?

I'd use the same technique for the other edge but a different adjacent length. Don't know if that makes sense without seeing the model so far.

yes right angle triangles but you need to figure out the leg opposite the rise as the circumference of the ramp in plan the hypotenuse is what you are trying to find to plot out on paper

LydiaM   to warp the triangle along the tube, divide your triangle vertically into thin units by drawing a light lines on the triangle , then cut above the line until you reach the bottom of the board, don't cut the bottom to keep the units connected... this way you'll be able to warp it easily.. and regarding the top parts, I think you'll have to draw as a circle first.. place it over your walls to see how it fit, then probably you'll have to slice it into many parts and place them in its' place above the walls since mountboard doesn't bend 

My (badly) made ramp. What I did was make the square end, the two triangular sides and the 'c' shaped base. I then put tracing paper on top flattened out and traced the tops of the sides and transferred it onto paper. I tweaked the paper to fit and make it more accuruate, then transferred it to mountboard. 

It's badly cut and a bit gluey but it's a ramp none the less! :P Thanks for suggestions guys, really helped!

for a height of 4m, what should be the length of the ramp for a circular ramp..?

In this case, you could not stretch the surface to fit. Your ramp is a helicoid, which is not a developable surface, i.e. it cannot be perfectly flattened onto a plane without distortions. Consequently, you will have to "discretise" the helicoid by cutting smaller segments to approximate its overall surface.

Assuming the ramp goes full circle or 360 degrees, if you want to keep it flimsy and very simple - like using paper / cardboard or mountboard only - as a suggestion, you can flatten the 2 cylinders (with 3m & 5m diameter, developed lengths = 3m x pi and 5m x pi respectively) and 1m high (scale down everything of course), then, on the resulting rectangles, draw the diagonals -> those will be the 3d spirals (helices) enclosing your ramp. Divide both diagonals in clearly marked and equal # of segments, same # for both, cut the areas above the diagonals, then coil back both rectangles (which by now are triangles) to achieve cylinders with original diameters, and position the cylinders in a concentric fashion as required to achieve the 1m wide ramp. This way you have the walls under the ramp, and at the top, the 2 helices divided in equal segments. If you divided them in say, 16 segments, you can now use the markings to cut 16 identical strips, located along the ramp to approximate the helicoid.