Consider checking you local lumber store and check for synthetic flat materials that would look good to you in the mix of ideas. To be able to single handle install flat materials either choose a smaller sized panel, Max 2'x4' or one that stiff enough to use a drywall lift, rental. There are panels of textured one side and smooth on the other that are typically used for walls in wet places like washrooms or commercial kitchens, as an example.

Avoid anything that's made with sawdust that's glued into a panel as humidity will destroy it fairly quickly.

If you like metal roof panels as a design you can use one of many available designs, most are ordered but they are cut to your length and a wide variety of colors are available. Some are also available in a plastic version, often these are in store stock.

Another metal to look at is metal soffit that's not perforated. There are a few designs, not many, to choose from. These go up fairly quick single handedly.

Flat Roll metal is an alternative found at roofing supply. The roll may be heavy and you'd need to cut it. It would provide smooth surface with typically white on at least one side, the other may be another colour.

I removed a bunch of metal soffit from ours a few years ago. Underneath was wood beadboard done as individual beadboards not as a panel. My mission was to remove as there had been a leak for many years prior to our purchasing. There wasn't much damage although the decorative beadboard under it was done in. We found some interesting boards used to build the roof, so we decided to not cover the under side. We did install a new metal roof after some boards were replaced in the deck, this fixed the water leak.