The self-reliant need a reliable earnings record. Of all the numbers lenders shuffle when they consider a borrower, the figure that lands at the top of the deck is the borrower's income. It wouldn't be prudent to extend you a loan for as long as 30 years without a strong possibility you'll have the earnings to pay it back.
Self-employed borrowers traditionally have scared lenders. Now, however, sophisticated computerized underwriting lets lenders pinpoint risk with greater accuracy, so they'll extend loans to the self-employed. But you'll generally need to demonstrate at least two years of earnings history before a lender will offer a competitively priced loan.
If you need a mortgage before that, an option is a "no" or "low" documentation loan. With the former, lenders ask no questions about your income, and with the latter, you state your earnings, but don't provide proof of the amount. With either option, you'll pay at least a quarter of a percentage point higher rate, and possibly much higher, depending on your circumstances.