Give the plot family a boolean variable, something like isSelected. When clicked set the variable isSelected to true for that plot. When the list of buildings comes up, build the selected one on the plot that is set to isSelected=true.
Logic will be something like :
Plot(family) on clicked, set family instance variable isSelected=true, load building menu.
Building (from menu) on clicked, create building at plot(family) where isSelected=true.
Plot(family) set isSelected=false. (clear)