大きい　大きな (difference and usage)
in what case which is used, what is the difference?

Question

Answer

In almost case, both are same meaning.
for example 「大きな箱」 and 「大きい箱」 are same meaning.

But in some case, 「大きい」 and 「大きな」 are not interchangeable.
for example 「彼は顔が大きい。」 is correct japanese sentence. but 「彼は顔が大きな。」 is wrong japanese sentence.

If you want to know detail, search at google with phrase 「大きい 大きな 違い」.
for  example,
http://www.alc.co.jp/jpn/teacher/soudan/015.html
http://detail.chiebukuro.yahoo.co.jp/qa/question_detail/q139291688

Answer

There is no difference. You can use whichever one you like.