Traditionally the outline courtyards would be squares, rectangles, circles etc. as this was the easily generated shapes for the CAD software used.
However, this can often leave blank areas of the PCB that could have a component in, but doing this would leave "component to component" errors as you'd have one inside another.
I.e. when you have a connector that has a big rectangular placement courtyard however it has big spaces where you can fit other small components without problem.
So AIUI the IPC7351-C courtyards now reflect the true shape of the components, this allows greater placement choices/ability where you can utilize unused space - which is more of a premium now things have got smaller.
The courtyards are explained in IPC-7351B near the first 1/4 of the doc.
If making a component manually I would always make a placement outline, used to enable me to place the components - this follows the contours of the component and used to be 0.5mm from the pad edges (assuming the pads are the extent - if not the physical component edge), then when placed I would get 1.0mm between pads of adjacent components (or component to component) - this used to be the rule of thumb distance for best placement and soldering/thermal distance. (taken from an old Siemens guideline document - prior to IPC standards.)
Things have changed (a long time ago) and now the distance is a lot less - depending if you use the least, nominal or most spacing's and the manufacturing class recommended by the IPC standards.
I would also add manufacturing values into this courtyard if for instance it was a tall component so that thermal shadows were not affecting others although this would generally be with a secondary placement outline, I also place assembly outlines on an assembly layer for the assembly documentation, silkscreen outlines (where required) on the silkscreen layer.
The more thought that you put into the creation of your components, what outlines will be needed, what shape and spacing they need to take, what layers they go on and where and when they will be used - the better your component library will be, the more accurate, the more useful and the easier your job will be.
This is why we use standards whenever we can, they maintain accuracy and consistency.
When you manually make components you need to calculate and draw your outlines yourself, although for the majority of your components you can now use the Library Expert program (there is a free version available) where you simply specify the values to be used and it auto creates all the outlines for you, the pads etc. Export them to your CAD package type and import them into a library.