Java (OpenJDK 8), 315315 306 bytes
i->{String r="";int j=0,k,u=i*2;char[][]c=new char[i][u+1];c[i-1][i]=95;for(;j<i;j++;j<i;r+="".valueOf(c[j++]).replace('\0',' ')+"\n")for(k=0;k<u+1;k++){if(k==j)c[j][k]=92;if(k==u-j)c[j][k]=47;if(k>j&k<u-j)if((i-j)%2<1)c[j][k]=(k-j-1)%2<1?(char)(47+((k-j-1)/2)%2*45):32;else if((k-j-1)%4==2)c[j][k]='|';}for(char[]l:c){for(char f:l)r+=f<1?" ":f;r+="\n";}return r;}