I'd rate this as a simple job to do - although you may need to fabricate a bracket to hold the expansion tank/bottle.
Parts can be found at your local breakers yard.
You need a japanese/korean car with a narrow plastic expansion tank. These MUST BE vented and NOT a pressurised unit.
I found a perouda item which is great and included the pipework from the radiator (total cost £3)
Fabricate a bracket/clip for the tank
Either use existing bolt holes beside radiator (near side of car) or make some new ones.
If you have access to rivet nuts then the holes are perfect
Connect pipework add coolant to top of radiator and to max line in bottle.
Now when the engine is hot the level in the bottle slightly increases and drops again to max when cold.
Dave[frame]