That’s what we call them. They could also be called mini geteldt’s.
Here’s a picture of the three we made so my kids could each have their own tent. There’s another picture in the Rectangular tent post.
They were made from unproofed canvas which we painted later with a waterproofing material from the canvas supplier. The fabric was much easier to sew, but the painting was difficult as we needed to find somewhere it didn’t matter if the compound soaked through. I now prefer to buy proofed canvas.
Here’s the picture we based the design/justification on. You have to look carefully, but there are two smaller tents. They could even be just the roof parts of a double bell tent. This is also the picture I’ve used for the Circus and Dining tents.
And here’s an indication of how to cut it out and sew it up. It’s just a rectangle with half a cone at each end. The line in the rectangular part is the seam we included to make it long enough to fit a bed between the poles.
A friend uses the Custom Pavilion Pattern Generator to work out the size of the pieces you need to cut to make the end cones.