Jan Waรenberg and Roland Wissel live on the 23rd floor of the Rheinstern high-rise in Cologne, they have so far lacked ideas for their terrace. They want a roof garden that fits their style of living โ and exudes the atmosphere of Southern California. This is the special challenge faced by gardening and landscaping expert Sebastian Burggraf and horticultural engineer Renรฉ Pรผtz.