Fiqh texts are made up of various components:
I. If we look at them compositely they contain:
- definitions
- rulings
- examples
- exceptions
II. If we look at them substantially, they consist of:
- textually gleaned understandings (i.e. from Quran and Hadith)
- issues of consensus
- opinions of the companions an/or their students
- opinions of the “Imam” of that particular school
- and at times opinions of the leaders of that Imam’s school after him
III. And if we look at them structurally then they consist of:
- chapters
- sections
- and subsections
With the latter being pretty obvious, the rulings that were expressed throughout those chapters, etc . and compose “Fiqh” were gathered to create a new form of text: al-Ashbah wa ‘l-NaZa’ir. These texts were not categorized like fiqh texts, even though they deal directly with the same substance of fiqh. Instead “ashbah” or “semblances” and “naZa’ir” or “relations” were correlated. Rulings that resemble each other were analyzed along side each other, and others which were related but did not have the same outcome were as well. From these the science of Qawaid Fiqhiyyah developed (for an excellent article on the subject look here). Some of these works were intra-school works, while others were comprehensive of different schools.
Other texts were created from Fiqh texts as well, such as the texts that deal with the “Mufradat” of a particular school and its Imam. Perhaps the most famous of all Imams in his “Mufradat” (i.e. issue in which he held a singular opinion) is Imam Ahmad Ibn Hanbal. This was for several reasons, one being that he was the latest of the four Imams to have a codified school gain prominence, as well as the fact that he was the one Imam from the four that narrated the most hadith, in addition to his keenness to collect the opinions of those scholars that preceded him, especially those of Ahl al-Hadith.
A third type of text was created out of fiqh texts, that of “Furuq” or differentiation between rulings, definitions, and exceptions. These works, although few in number, detail the differences between seemingly similar things, their exceptions, and the reasoning behind that. These texts are closely related to those of “Qawaid fiqhiyyah” and as such many of the early authors of such texts were those that gained prominence for their “Qawaid” writings in both fiqh and Usul.

This is a great idea Joe; I have always found the structure and internal logic of fiqh texts to be very interesting, and mapping it out to understand the coherence of such texts sounds like it would be very useful for people like me who have not had formal training in the discipline.
Will you also touch on usul al-fiqh texts and those which “bridge” the divide between such as takhrij al-furu` `ala al-usul? Mapping how the various genres of texts all fit together comprehensively would be an amazing project, and no doubt very useful as I have seen very little in English discussing this!
So far I have about 4 posts in the series, so we’ll where it goes! Glad that this interests you and hope to hear more from you and others.