the type of pump you are using is a very important factor as that determines the volume supplied and the pump curve (pumps lose their effect over long distances dependant on tpye), however, google 'boxes formula', this is used for calculating  diameters of supply pipes. If that crazy calculation throws you
Then reckoning can be used. I reckon with my almost expert opinion (been Qualified 22 years) run the largest dia. you can ie; 32 all the way, if not then 1x25m  roll of  32mm and 1 25m roll of 25mm the cost difference between 25 and 32 aint that great from your rural supply merchant, they're often cheaper than plumbins supply merchants. p.s. if you oversize now you will be able to increase the size of you house later.