You have to follow some set of rules to design any structure. It takes me maybe about a half hour to lay out every single timber on an elevation like this if I have any kind of idea in my head of what I want beforehand.
This is a system of designing the structure as a whole. This is a system that may have been used by the ancient Greeks, at least the Romans, and some evidence suggests that the Egyptians used this or something very similar, and it fell out of favor and eventually died out altogether during the Renaissance.
The rules in this system exist because you have to have rules. If I gave you a pen and a piece of paper and told you to draw me and accurate layout of a building, one accurate to be used to find all the measurements, would you be able to do it? Would you be able to make it square, and make it exactly the right width, height, etc. or even close? Would you be able to do that with JUST a pen? The answer to all of those questions is no.
Therefore you have to have some other tools. To keep matters simple, this tradition has inserted just 2 other tools, a straightedge and a compass. The rules exist so that you can know how to use these tools to get desired results. If I handed you a compass and a straightedge and told you I wanted a building, would you be able to do it? Not without some kind of a system to use these things. And that's all these rules are.
These 'rules' are realities that are inherent in the system. one 'rule' is that I must set the compass radius to some dimension that is found on the diagram. This sounds like a limitation, but in reality it's absolutely necessary. Otherwise you would have totally arbitrary dimensions with no relationship to each other whatsoever. That's a recipe for disaster. And if you can't find a dimension that fits the bill, either plot some other parts until you do, or else use your compass and straightedge to create some new lines and circles. piece of cake. Think of these not as rules, but as instructions on how to arrive at a desired result.
Really this system is not complicated at all, it is amazingly simple.
What do I mean?
Well consider the alternatives
If I want to lay out a building by modern methods, then I use a ruler to establish known measurements, sure (or tell a computer to make a line of a given length) Then I make more measurements and so on, and then something strange happens. I have to sit down and do some figuring. That's right, mathematics. That's complicated. Especially when you get into roof design and truss layout and all that good stuff. Pretty soon you either need a good computer program or else some sound knowledge of trigonometry. That's complicated.
I can do the same thing with my compass, believe it or not, without once writing down a single number or opening up my calculator. That's simple. I can design a great cathedral with such accuracy, and geometric relations that defy computers and modern architecture. I can make an infinite array or fantastic structures, from the Barns at Cressing to the great Cathedrals of Europe, to the awe inspiring Hagia Sophia of Constantinople (it will always be Constantinople to me, Istanbul just doesn't quite make it I'm afraid) and the list goes on to just about anything built from the reign of Rome to the Renaissance.
This all is not to make you feel bad or wrong, it's to show that these 'rules' are inherent to any system, and quite necessary if you want to do anything good. Any way you design a building is set with a certain set of rules, otherwise you really can't do anything much at all. You have a set of rules that tell you how to determine where to place your floor joists or bents or rafters or.... So do I, I just have a different set, that's all. Or do we place one rafter here, 2 feet from the end wall at this pitch, then place the next one 5 and a half feet away from it at another pitch? Of course not, we follow the rules or the structure will suffer.
Imagination is all well and good, but it too has its own set of rules it must follow, although those rules are different for each person.
