He commissioned work on the old building from Leone Battista Alberti and Bernardo Rossellino and also had Rossellino design a plan for an entirely new basilica , or an extreme modification of the old .
Pope Nicholas V , ( 1447-55 ) , was worried about it and got two architects , Leone Battista Alberti and Bernardo Rossellino , to make plans to restore it or build a new one .