Provisions for professionals

Yes, he can declare income u/s. 44ADA, as 50% or more, without books of accounts, no audit required.

For less than 50% profit margin, he has to keep books of accounts as prescribed under section 44AA along with Rule 6F. File form ITR 3 with BS & P&L accounts. And tax audit required.

Proviso to Rule 6F (1) provides that if the gross receipts of a profession do not exceed Rs 150000 in any one of the three years immediately preceding the previous year or where the profession has been newly setup in the previous year, his total gross receipts in the profession for that year are not likely to exceed the said amount, then such professional need not to maintain any books of accounts as mentioned in rule 6F. 

It means that if the gross receipts of a profession exceed Rs 150000 in all the three years preceding the previous year only then the books of accounts will be required to be maintained, if the gross receipt exceed the prescribed limit in the two preceding years but not in the third preceding year then there will be no need to maintain books of accounts as contemplated in rule 6F.

Failure to maintain books of accounts and other documents or to retain them as required u/s 44AA attracts penalty of Rs. 25000 u/s 271A.  The penalty can be imposed by the assessing officer or CIT (Appeal)