Charcoal, 17 13 bytes

Thanks to @Neil for saving 4 bytes!

(↙↓⊖θＭ↑(→↗Ｎ‖Ｍ

Try it online!

Explanation:

(↙                // Print '(' and move one step down and to the left.
  ↓⊖θ             // Print n-1 '|'s downwards.
     Ｍ↑          // Move one step up.
        (→        // Print '(' and move one step to the left.
          ↗Ｎ      // Print n '/'s towards the upper right corner.
            ‖Ｍ    // Mirror the left half to produce the right half.

Charcoal,   17   13 bytes

Thanks to @Neil for saving 4 bytes!

(↙↓⊖θＭ↑(→↗Ｎ‖Ｍ

Try it online!

Explanation:

(↙                // Print '(' and move one step down and to the left.
  ↓⊖θ             // Print n-1 '|'s downwards.
     Ｍ↑          // Move one step up.
        (→        // Print '(' and move one step to the right.
          ↗Ｎ      // Print n '/'s towards the upper right corner.
            ‖Ｍ    // Mirror the left half to produce the right half.

Charcoal, 17 13 bytes

Thanks to @Neil for saving 4 bytes!

(↙↓⊖θＭ↑(→↗Ｎ‖Ｍ

Try it online!

Charcoal, 17 13 bytes

Thanks to @Neil for saving 4 bytes!

(↙↓⊖θＭ↑(→↗Ｎ‖Ｍ

Try it online!

Explanation:

(↙                // Print '(' and move one step down and to the left.
  ↓⊖θ             // Print n-1 '|'s downwards.
     Ｍ↑          // Move one step up.
        (→        // Print '(' and move one step to the left.
          ↗Ｎ      // Print n '/'s towards the upper right corner.
            ‖Ｍ    // Mirror the left half to produce the right half.

Charcoal, 17 bytes

(Ｍ↙↓⁻θ¹Ｍ↑(Ｍ→↗Ｉθ‖Ｍ

Try it online!

Explanation:

(                  // Print '('.
Ｍ↙                // Move one step to the down and to the left.
↓⁻θ¹               // Draw a line of n-1 '|'s downwards.
Ｍ↑(               // Move one step up and print '('.
Ｍ→↗Ｉθ              // Move one step to the right and print a line of n '/'s.
                   // Now the left half of the shield is done.
‖Ｍ                // Mirror and copy the left half to finish the shield.

Charcoal, 17 13 bytes

Thanks to @Neil for saving 4 bytes!

(↙↓⊖θＭ↑(→↗Ｎ‖Ｍ

Try it online!