Roofs and water collection query.

I'm a bit dubious on that point, but adapting your rubbish drawing into my rubbish drawing!


the distance between Red (Pent roof facing the rain) and Blue (facing away from the rain) there appears to be a wider catchment when Red / facing the rain.

 

No need for a drawing if you think back to geometry at school - the length of the hypotenuse is always greater than that of the adjacent and opposite. So if it's facing away from the rain the angle of incidence becomes more oblique and less rain is collected.

 

But if it falls (equally?) between vertical and 45 degrees and comes (equally?) from NSEW, you have sufficient capacity in your butt(s) so they don't surcharge in downpours, you get 0.85m of rain p.a., it falls equally throughout the year, your shed is 3 x 2.4m on plan, you only use the water in the garden from June to September inclusive, then the amount of extra rainfall you might gather p.a. from a monopitch roof is about 7 two gallon water cans, which over 4 months is about 1 gall/week.

Would anybody notice the extra?

 

... unless you also collect the water running down the shed walls

 

Let's look at this from a different angle if you'll excuse the pun! If the shed in question was going in my garden I'd let the site of where it would be make the decision on what type of roof. If the shed is going to be sheltered by perhaps trees it's not going to make any difference how that rain falls and on what type of roof. If the shed is going against a boundary and it has a pent roof which tends to slope backwards it's not going to make it easy for access to the guttering and feed to the said butts.

Rain aside and looking at the practicalities of the interior I'd choose an apex every time. There's always something that's to large to store anywhere but in that apex and with a pent roof it will have to be at the front of the shed probably in front of a window. I've had both types and prefer the apex. However, I have no rain butts, I don't need them, so perhaps I should 'butt' out of this conversation. Let's face it I shouldn't think there's that much difference in rain collection to worry about which roof is chosen.