a big congratulation vs a big congratulations

Some examples from the web:

• A big congratulations to our fundraising champion.
• So those thugs are chasing you down to give you a big congratulations?
• This is such a big deal. Congratulations.
• I must therefore say thank you - a big thank you - and congratulations to Mr Evans, who has done some very substantial, first-rate and persistent work in connection with this report.
• An article thus big, congratulations.
• You know how to shoot little people with big guns, congratulations.
• Big O, big ups and congratulations... playboy player.
• Congratulations, Big Daddy, on your birthday.
• Congratulations. You've been a big help, for once.
• Congratulations. This is a big deal.
• Congratulations, you are a big boss now.
• Congratulations. It's a big deal.
• Congratulations, man. That's a big deal.
• Congratulations. Today's a big day!
• Congratulations to our cake... that won a big fat nothing!
• A big 'thank you' to the President and, once again, hearty congratulations: you deserve to celebrate, and not just with a beer.
• You've made a big mistake trying to escape, a big one.
• This will turn a big transmitter into a big receiver.
• A big man with a big mustache.
• A big tree is too conspicuous, a big forest on the other hand...

Some examples from the web:

• So those thugs are chasing you down to give you a big congratulations?
• A big congratulations to our fundraising champion.
• This is such a big deal. Congratulations.
• I must therefore say thank you - a big thank you - and congratulations to Mr Evans, who has done some very substantial, first-rate and persistent work in connection with this report.
• An article thus big, congratulations.
• You know how to shoot little people with big guns, congratulations.
• Big O, big ups and congratulations... playboy player.
• Congratulations, Big Daddy, on your birthday.
• Congratulations. You've been a big help, for once.
• Congratulations. This is a big deal.
• Congratulations, you are a big boss now.
• Congratulations. It's a big deal.
• Congratulations, man. That's a big deal.
• Congratulations. Today's a big day!
• Congratulations to our cake... that won a big fat nothing!
• A big 'thank you' to the President and, once again, hearty congratulations: you deserve to celebrate, and not just with a beer.
• You've made a big mistake trying to escape, a big one.
• This will turn a big transmitter into a big receiver.
• A big man with a big mustache.
• A big tree is too conspicuous, a big forest on the other hand...