You can’t create meshes inside Roblox Studio, but you can create them inside Blender 3D (and export them into your project). Blender 3D is a free program under the GNU Public License.

Best we have right now. Exporting from Blender to import to OpenSim without plugins. This may work for Second Life as well but I haven't tested it. While working in Blender, it's better to orient your ...