##Javascript (ES6), 97 85 81 75 bytes
n=>(g=(n,s)=>n?g(--n,`|${" ".repeat(n)}\\\n`+s):s)(n,"")+"-".repeat(n&&n+1) Turns out I wasn't using nearly enough recursion
f=n=>(g=(n,s)=>n?g(--n,`|${" ".repeat(n)}\\\n`+s):s)(n,"")+"-".repeat(n&&n+1) console.log(f(0)) console.log(f(1)) console.log(f(2)) console.log(f(3)) console.log(f(4))