:confused: how to build an interior round wall.

Would you please describe in a little more detail as to what you are wanting to do, please? Like, where the wall is to be located? Is this a wall from the floor to the ceiling? Are you going to be tearing out an existing wall? Thank you!

It is a new wall from cement floor to unfinished ceiling in a basement

I'm going to assume you now how to find an arch on a piece of plywood, if you don't ask me and ill give you those directions. Use a piece of 3/4 ply, doenst have to be a good grade of wood, but the bottom half needs to be treated plywood,
depending on how long of a arch or round wall you need will determine how many plywood rips you need,

its best to lay the plywood down and find the center of the board , mark this, now you can either get you a string or a staight edge to hold the pencil, which ever you do your making a pivet point, if you use a piece of wood then nail it on the center of the plywood near the bottom edge at the top is where you hold the pencil or drill you a hole that the pencil will slide down in, once this is set up make a mark, this will give you an arch. Measure down or up if you have room to 3 1\2" same as a 2x4 rip this same piece again, when this is done you now have 1 arch youll need to have 4 of these one of which needs to be treated for the floor. screw them together with 1 1/4 screws. once you have the first one cut out just use it as a template and cut the others,

after you get it laided out on the floor saying its the right size, youll need to add the 2x4 studs, hold them flush with the edge , theyll be turned so edges dont stick out past the archs youve cut, 16" on center may not be enough so id go every 12" on center with the studs,
as for sheetrock to cover it, you be best in using 1/4, to bend around this, 1x2 want work unless you wet it down and 3x8 is just about the same.

if you need a bigger arch you'll need to use more plywood and a longer straight edge or a longer pencil, which ever you used before. Try and butt 2 sheets together and this will give you a longer arch. Good luck.
if you type in how to make arches or circles you'll find pics of this.
also at Lowe's they make a dowel rod that holds a pencil just for this puropse its around 10bucks. Its short so you'll have to buy a new dowel rod to make bigger arches but its cheap to.good luck