so - such 

        So       is used before an adjective or an adverb (so big,  so carefully)

        Such,  followed by a or an, is used before an adjective+noun (.. such a long time)  

                                             ◊   This book is so interesting.
                                             ◊   This is such an interesting book.

                                             ◊   Julie's new house is so big.
                                             ◊   Julie has such a big house.

                                             ◊   He drives so carefully.
                                             ◊   He is such a careful driver.

                                             ◊   You are so clever.
                                             ◊   You are such an intelligent person.