Outlining the Epistle to the Roman Church is no easy task. Few scholars agree with every jot and tittle of another scholar's outline of Paul's masterpiece.
Douglas Moo, in his fine technical commentary, argues for an outline following a conglomeration of different guidelines for ancient letters while Luke Timothy Johnson and Robert Jewett argue that Romans should be viewed as a piece of ancient rhetoric. I think Johnson and Jewett have the stronger argument. Few ancients could read and Paul's letters, with the exception of the epistles to Timothy and Titus, would have been read aloud to the congregation by someone in the congregation who possessed some education.
Ancient rhetoric was taught in every school in the Roman world. Paul almost certainly attended the fine university at Tarsus and, thus, would have been educated in the ancient art of rhetoric. The discipline had fairly strict rules. Each speech, with some notable exceptions, was expected to contain an exordium (an introduction that contained key themes and sought to favorably dispose the audience to the forthcoming message), a narratio (a brief statement of relevant facts), a propositio (a brief thesis statement), a probatio (a supporting argument), and a peroratio (conclusion aimed at stirring the audience to action).
I believe Paul followed the rules of ancient rhetoric and structured Romans as following:
Exordium (introduction) 1:1-12
Narratio (facts) 1:13-15
Propositio (thesis) 1:16-17
Probatio (argument) 1:18-15:13
Peroratio (conclusion) 15:14-16:23
Read through Romans using a reliable reader friendly translation such as the New Living Translation (find it over at Biblegateway.com) and see if you agree.
Blessings to you all.