How can I make curved gingerbread sheets for a gingerbread house? I'd like to make a single cylindrical tower for my gingerbread house this year, about 8 inches in diameter and probably 6-8 inches tall.

This doesn't have to be made in one piece. I'm fine with building it out of 2-4 curved pieces and seaming them together.

What I do not want is to use many flat gingerbread pieces and end up with an octagon or dodecagon that "pretends" that it's round.

The goal of this is to find out a good method for making curved sheets of gingerbread by either shaping them while baking or after.

I'm planning to use Stella Park's recipe for gingerbread to be used for construction, which notes that it's soft (for cutting purposes) when removed from the oven, but I'm not sure if that's soft enough to try to shape after baking, too.
Not knowing your recipe too well I’ll assume a gingerbread with a rollable and cuttable texture, like for gingerbread men. 

I would use a few empty cans with a slightly smaller diameter than your tower design. 

If you cut the can(s) lengthwise in thirds or so, you can drape rectangular strips of dough over them with only some bend, which will put only little  gravitational stress on the soft dough during baking. Make sure that the total width of the segments is more than the 360 degrees circle to allow for shrinkage and some extra to cut the edges to fit.

Bake the dough on the molds (with a layer of parchment, ideally) and let the parts cool on the tins as well. 

Assemble as you would for the straight walls. A spare can can help keep the parts upright and in shape until the icing “cement” has hardened.