We make exclamations using HOW and WHAT
 
HOW + adjectives / adverbs

- How nice!
- How nice it is!
- How tall that tree is!
- How big your house is!
- How fast!
- How fast the train goes! (= the train goes very very fast)
 
  WHAT (a) + nouns

the article "a" is only used with countable singular nouns, as usual
 
- What a surprise!
- What a big house you've got!
- What stupid things you say!
- What beer!

since they're not questions, there is no inversion!!!

- How big that tree is ! What a big car you have ! (exclamation, no inversion)
- How big is that tree !
- How big is that tree?  (question, inversion)

Compare:

- How beautiful she is  (how + beautiful: adjective)
- What a beautiful girl she is  (what + a beautiful girl: noun)

Click here for SO / SUCH for exclamations