I don't know of one either but you need to start by measuring your garden accurately and drawing it to scale including orientation so you can see where sun and shade will be.
Then make a list of things you want and don't want - terrace, sunny seating/dining area, shaded seating/dining area, pond, pergola, arbour, shed, greenhouse, work area for potting/compost/cold frames, BBQ, trampoline, Wendy house, dog run and so on. Draw some of those t o scale and cut them out and shuffle them around on your plot plan.
Then look at what you need to disguise - neighbouring buildings and windows or eyesores and also confirm your soil type as this will affect things like chocie of plants for drainage, alkalinity or acidity, lawn or gravelled or paved area........
Have a read of this info from the RHS and follow the various links -
https://www.rhs.org.uk/advice/design?awc=2273_1587141826_d03cd7a5f44188d30766c234e4e10a4aLots of garden design ideas on Pinterest too.