I have little knowledge about plumbing systems for what is required and I am designing my own self build. What sort of space is needed for items? I have given space for a boiler but im not sure what other items are included in the systems, like will I need a water tank in the roof? I have an inhabitated loft with a bathroom up there, so does it need to be higher than everything or can it he hidden in the eaves?

Tanks in the loft are last centuries plumbing. Either fit a combi boiler, or unvented water tank that as it's name suggests runs at (close to) mains water pressure so needs no header tank.

 

Apart from not needing a tank, it is so much better to be able to have a shower with decent water pressure.