I build the hardscape then take a photograph. I edit photographs on MS paint. I usually draw the lines, focal points, colors and plant positions. If the hardscape sucks then I start again.
You can see in the thumbnail that I started with the black lines to get a geometrical arrangement.
Working in 3D is better.
Besides looking at other aquascapes and getting ideas Taking photos while out and about in the countryside, coastal views etc can give you inspiration. Often advised by Amano. A scape box then to develop your scape ideas