I have a plan... but need help

Hi
I’m in really need of help and advice.
I’ve designed and started to build my rear garden (see attached) the garden is SSW facing . I can't use those 3D design things so will have to put up with my sketch. LOL
The trouble is I want to plant it based on ferns, grasses, hostas, acer, palms type plants but have absolutely no idea what will work where layout etc . Please please can you or anyone help out.

Click image to enlarge