I have a brownie tin that is the perfect shape for my next cake but it is only about 1 inch deep and has sloping sides. I’m wondering if it’s possible to build the sides up with parchment paper to bake a taller cake. I have some paper that is like foil on one side and quite stiff that might work. Does it sound possible?

Yes, you can line the sides with parchment paper, but it is hard to get it to stand up straight (but not impossible) when the sides are sloped.  Once baked, you can trim off that little extra bit of slope.  You could also bake the cake in two thinner layers and save the trouble of torting.