以自定义比率和间距排列ggplots

I am trying to combine n number of barplots with one common label plot at the bottom. My problem is that grid.arrange combines the two plots in 50%-50%. I am looking for something like the layout matrix where you can specify 4 slots and first 3 to be taken up by first plot and last slot by second plot. And customise similarly depending on number of plots.I am trying to combine n number of barplots wit