@checks = (1, 3, 5); #just inserting some values

my $cnt = 0;
foreach (@checks)
{
  $cnt++;
}

if ($cnt == 1)
{
  fields =>
  {
     'field1' => 'value',
     'field2' => 'value',
     'checkfield' => '1'
  }
}
elsif ($cnt == 2)
{
  fields =>
  {
     'field1' => 'value',
     'field2' => 'value',
     'checkfield' => '1',
     'checkfield' => '3'
  }
}
elsif ($cnt == 3)
{
  fields =>
  {
     'field1' => 'value',
     'field2' => 'value',
     'checkfield' => '1',
     'checkfield' => '3',
     'checkfield' => '5'
  }
}