All in all it's just, uh, another trick in code golf

C, 86 85 83 82 bytes

3 bytes saved thanks to Lynn.
1 byte saved thanks to charlie.

i;f(o,w,h){++w;for(i=0;++i<w*h;)putchar(i%w?i/w%3?i%w+i/w/3*4+~o&7?32:124:95:10);}

C, 92 bytes

b(f,w,h,y,x){for(y=0;y<h;y++,puts(""))for(x=0;x<w;x++)putchar(y%3?(x+y/3*4-f)%8?32:124:95);}

Invoke as b(F, W, H).

Pyth, 43 27 bytes

I need to golf it heavily... the score is too shameful.

AQVE<*H?%N3X*8d+G*4/N3\|\_H

Try it online already.

Input format

6,44
11

Output format

____________________________________________
      |       |       |       |       |     
      |       |       |       |       |     
____________________________________________
  |       |       |       |       |       | 
  |       |       |       |       |       | 
____________________________________________
      |       |       |       |       |     
      |       |       |       |       |     
____________________________________________
  |       |       |       |       |       | 

Explanation

AQVE<*H?%N3X*8d+G*4/N3\|\_H   First two inputs as list in Q,
                              third input as E.

AQ                            Assign G to the first item in Q
                              and H to the second item in Q.
  VE                          For N from 0 to E-1:
                   /N3            N floor-div 3.
                                    if N gives a remainder of 3 or 4 or 5
                                    when divided by 6, this will be odd;
                                    otherwise, this will be even.
                 *4               Multiply by 4.
                                    if the above is odd, this will leave
                                    a remainder of 4 when divided by 8;
                                    otherwise, the remainder would be 0.
               +G                 Add G (as an offset).
           X*8d       \|          In the string "        " (*8d),
                                  replace (X) the character with the
                                  index above with "|" (modular indexing,
                                  hence the manipulation above).
       ?%N3             \_        If N%3 is non-zero, use the above;
                                  otherwise, use "_".
     *H                           The above repeated H times.
    <                     H       Take the first H characters of above.
                                  Implicitly print with newline.