Create a percent sign

JavaScript (ES6), 52 bytes

n=>[...Array(n)].map((_,y,a)=>a.map(_=>y++%~-n<1|0))

Jelly, 6 bytes

²Rm’Ṭs

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How it works

²Rm’Ṭs  Main link. Argument: n

²       Square; yield n².
 R      Range; yield [1, ..., n²].
   ’    Decrement; yield n-1.
  m     Modular; yield every (n-1)-th element of the range, staring with the first.
    Ṭ   Untruth; yield a Boolean array with 1's at the specified indices.
     s  Split the resulting array into chunks of length n, creating a matrix.

V, 15 bytes

Àé ÀÄ|r#L.|ò.kl

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Explanation

Àé<space>        " Argument times insert a space
ÀÄ               " Argument times duplicate this line
                 " This gives an arg-by-arg matrix of spaces
                 "  and brings the cursor to the end of the first line
|r#              " Go to the beginning of this line and replace the first character with #
L.               " Go to the end of this matrix (bottom-right corner) and replace that character with a #
|                " Go to the beginning of the last line
ò                " Recursively do:
 .               "  Repeat the last action, r#, replace the character under the cursor with #
 kl              "  Go 1 up and 1 right