There are lots of ways up the mountain...each with their own advantages and disadvantages.
Easy Helix offers a stacked, cylindrical-shaped helix in kit form. I believe theirs is intended for HO but could easily be used for N scale. The one on their website has a 68" outside diameter with 2.1 and 2.3 percent grades that rise 2, 6, 10, 14, or 18 inches (more in 4 inch increments). Their stacked helix takes up 32 square feet of real estate and, at 4.5 turns for $230 + shipping, might seem too pricey to some modelers, but worth it for others who don't want to do their own design and component construction.
This calculator is designed to help N-scalers who want to build their own bowl-shaped helix to fit their personal givens and druthers. It automatically determines critical dimensions for a bowl-shaped helix as a function of the specific preferences entered by the modeler. With judicious use of grades before and after the helix, it is possible to rise a considerable distance without going beyond a 48 inch diameter (i.e., the helix footprint could fit in a 4 ft by 4 ft space--16 sq ft). The entire ramp and a 4x4 ft support base panel could potentially be cut from a single 4x8 sheet of plywood and the vertical supports and tangent ramps from another 4x8 sheet...perhaps $100 for a 5 or 6 loop bowl-shaped helix.
Take a look at my blog entries on bowl-shaped helix construction and at Hemi's and Cleggie's threads on their layout construction.