Adjectives: position after as, how, so, too

After as, how, so, too and this/that meaning so, adjectives go before a/an. This structure is common in a formal style.

as/how/so/too/this/that + adjective + a/an + noun

I have as good a voice as you.
She is too polite a person to refuse.
How good a pianist is he?
I couldn't afford that big a car.
It was so warm a day that I could hardly work.

The structure is not possible without a/an. 

I like your country - it's so beautiful. (NOT I like your so beautiful country.)
Those girls are too kind to refuse. (NOT They are too kind girls to refuse.)

[source: Practical English Usage]