I say built-up because they're a box with breakers mounted in it, with no bus-bar; all the wires jumper from breaker to breaker. Breaker lugs are used as splice points with many many wires terminated in each lug.
Most regulations leave it to the breaker manufacturer to state whether double-lugging is acceptable or not. Typically breakers are rated for up to two wires of the same cross-section!
Bus bars are used as an independent part of the panel assembly, usually provided by the breaker manufacturer. They are usually a set of three copper bars with spade connectors for every breaker enclosed in plastic. Covers for empty breaker spaces as well as both ends of the bars are required. Where double pole breakers or RCDs are installed, the phase tab of the bus bar is removed in the field, either sawed off or broken with pliers (some manufacturers provide breaks there). These bus bars need to match the installed breakers and are typically rated for up to 63 amps. Solid or stranded wire links are perfectly acceptable too but take more time to install. At least Hager and ABB provide bus bars that just snap into the breakers. Non-matching breakers can be installed but usually don't fit the bus bar and have to be connected using jumper wires.
Hardly any country has mandatory phase colors, usually anything but yellow/green can be used, where a neutral is present it has to be blue (though this seems to have been omitted in Iraq and replaced with black).
Grounding can either be achieved by bonding to the neutral (at any point of the given install, depending on age and location) even without a local ground rod (TN-C system) or only to a local ground rod (TT). TN-C systems can have the neutral bond anywhere from the service entrance to the last receptacle. In most countries the neutral ahead of the bond (called PEN for protective earth neutral) is required to have a cross section of no less than 10 sq. mm. to minimize the risk of a broken neutral (which would result in all grounded surfaces becoming hot in case of an unbonded ground). It is regarded as good practice to bond as early as possible though.
Typical checks include isolation resistance, ground and loop impedance and RCD trip currents/times.
Voltage drop is regarded as a big issue, especially in Germany. Total voltage drop from the meter to the last fixed device is limited to 3% and in theory an electrician would be required to calculate the cross section of any(!) wiring run based on mechanical strength, wire ampacity (depending on cross section and type of installation, e.g. non-metallic cable or wires in conduit embedded in insulation, wires in conduit in solid walls or surface mounted conduit, non-metallic cable directly embedded in solid walls,...) and voltage drop.
In everyday work there are rules of thumb valid to wire runs no longer than 30 meters, above a quick voltage drop calculation becomes adviseable.
RCDs have a maximum current on the name plate and if either the upstream OCPD or the sum of the downstream OCPDs exceeds the rating the have to be protected by a suitably rated OCPD!
Some countries have differing requirements regarding this point, Switzerland allows for protection exceeding the RCDs rating based on the assumption not all loads will be run simultaneously, Austria on the other hand requires the RCD nominal current to be equal or greater than 1.6 (main fuse) or 1.45 (main breaker) times the nominal current of the priotecting OCPD.
That's all I can think of now.
