Trellises for indoor houseplants don't have to be as sturdy as trellises for outdoor plants. Indoor plants usually don't grow as large as outdoor plants and they also don't have to tolerate high winds like outdoor plants do. You could build a small trellis for an indoor plant that looks like an outdoor garden trellis, but look for unusual objects around the house that you can use for trellises for houseplants.
Use large wooden spoons for a table-top size plant in the kitchen. Use the longest wooden spoons you can find and insert them into the soil with the spoon-end up. Group them together in the center of the pot for a plant that will be seen from all sides. Place the wooden spoons along one side of the pot and allow the plant to climb upon them. This gives an effect similar to an outdoor trellis that is set against a wall or fence, with the plant material all in front.
Plastic Clothes Hangers
Re-purpose plastic clothes hangers by inserting them sideways into the soil. This will work for a small to medium sized potted houseplant. For a larger plant, wire them to each other so they are stacked vertically, making a taller trellis. Or make a more complicated trellis by wiring several together in a pleasing design. This is a good idea for a bedroom or dressing room.
Branches from Trees or Shrubs
For a rustic look, collect branches from trees or shrubs that have interesting colored or textured bark. These can be as large or as small as needed for each houseplant. White birch trees and crape myrtle shrubs both have interesting peeling bark with a lot of interesting texture. Red twig dogwood has a bright red color. Remove any side branches for a single post or leave the side branches for a fanned out effect.