Click on wall, later do Ctrl+T, choose func_brush and name wall. Later go entity, which will decide about wall appearing and dissapearing, click "Outputs" and in "Targets entities named" add name, which you named wall and in "Via this input" choose Disable to disappear, or Enable to appear
Yes. Make wall, select it, press CTRL+T and make it func_brush. When you give it a name you can disable and enable it with inputs E: God damn it. SC PL wrote excatly same time than me. I saw his post just when I finished mine