Thanks Carroll, Ed, Don and Henry.
Ed, the landscaping - terrain - was made in Turbocad, because Sketchup often makes a mess of my Autocad files. The building was modeled in Sketchup and terrain and building were imported in Vue 7.5 Infinite.
There I changed or adjusted some materials (e.g. the water) , "painted" some trees in the background with the "Ecopainter"- a special tool in Vue - and added a car.
The whole scene was then rendered 2500 x 2500 pix in radiosity at the same time creating selection channels of the materials used.
These selections were used in Photoshop to manipulate things like pavement, glass, grass, etc.
The sky was removed and replaced by a photograph I preferred after looking at the render result.
People and plants were added in Photoshop. These are alpha channel images ( no background) which can be scaled to proportion.
I hope this gives you an impression of my workflow.