There’s several methods for making sword blades. I would say that starting with a wooden dowel as the base that can run through the center of the sword for stability and to base the hilt off of is a good idea.
For materials, EVA foam, carved wood, and plastic are the most common. This type of sword can possibly be made with flat or mostly flat pieces of your material in a prism shape over the center meeting at the edges, or you can carve and/or heat form materials around the center.
Since there are so many possible methods for this type of prop, I’m going to link here our compendium of sword tutorials, since I am sure that this will help give you some ideas:
I hope that helps! Good luck :]