Resizing a single subplot in matplotlib

Resizing a single subplot in matplotlib

I'm having trouble trying to resize one of my subplots in matplotlib.
Basically I have four plots and I would like the to be about 1.5 the size
of the others.
I'm also having trouble trying to gives a legend for the top subplot. I
would like it to specify each colour as 1, 2, 3, 4, or 5 (Please see
image).
This is my code for the plotting function
def plot_data(avg_rel_track, sd_rel_track_sum, sd_index, sd_grad):
fig, (ax0, ax1, ax2, ax3) = plt.subplots(nrows=4, figsize=(15,10))
fig.subplots_adjust(top=0.85)
ax0.plot(avg_rel_track_nan)
if len(sd_index)!=0:
if len(sd_index)>1:
for i in range(1, len(sd_index)):
if sd_grad[i]==1:
ax0.axvspan(sd_index[i-1],sd_index[i],
edgecolor='#FFCC66', facecolor='#FFCC66', alpha=1)
#The following plot has 5 plots within it.
ax0.set_title('Averaged Relative Track',fontsize=11)
ax0.set_ylim(auto=True)
ax1.plot(sd_rel_track_sum)
ax1.set_title('RT Standard Deviation',fontsize=11)
ax1.set_ylim([0,250])
ax2.plot(splitpre)
ax2.set_title('Track Split',fontsize=11)
ax3.plot(ts_sd)
ax3.set_title('Track Split Standard Dev',fontsize=11)
ax3.set_ylim([0,100])
fig.tight_layout()
plt.show()
I am struggling to find a way to resize without changing the whole way the
function is written. I can't seem to find the documentation for
'subplots'.
Also to my understanding you must add a 'label' to your plot in order to
create a legend. However, all the data to the top subplot is plotted at
the same time?