to me it looks as ideal a spot as any.
yes maybe there is a tree near by, but theres not many ponds completely free of over hanging or nearby trees.
you have the added advantage of a hedging back drop, which will provide cover and habitats for many wild species, and also the side of your shed/garage which will have many cracks, crevices and holes for newts etc to hide within.
afew leaves in autumn will rot down and form a nice loamy layer on the bottom for the pond for plant life to root into, and anchor itself, which is a real plus point.
your water quality should be just fine, an fairly even mix for sunlight and shade will keep the water clean, clear, oxygenated, and perfect for allsorts of wildlife.
i'd be inclined to incorporated abit of rockery or dry gravel areas submerging into the water to enable frogs/toads/newts etc access into and out of the water, and not forgetting an easy way out for the unfortunate mr hedgehog who falls in whilst on his travels under the cover of darkness.
you may also consider running some wild meadow turf just to the the waters edge, giving both a natural look and sloping sides.
hopefully thats given you some help and suggestions