update: thanks to blakem for his hint below. And I hasten to add that if the vars are allowed to be pre-defined, then it's 135.
Alas, the best I can do is 148 146:

sub
golf
{
#        1         2         3         4         5
#2345678901234567890123456789012345678901234567890
($h,$f)=@_;$w=$"x($h-1);$_="$w=$w\n";@a=qw/0 @ + *
/;push @a,'=' for(1..4/$f);$p.=$_ while s/ (=+) /=
$1=/;$p=~s#=#$a[rand 4/$f]#eg;print"$w*$w\n$p"
}

$golf(10,0.3);

         *
        =@=
       =+==@
      @=@=0=+
     ==+===@=*
    ==========0
   0===0*=@*=@+=
  =+======@@====+
 =====+=@====0====
===@======+*+*=+==*
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§ George Sherston