Save output dynamically in a for loop in another dataframe (pandas)

Question

I have 2 lists

brand = ["Old Wild West","Rosso Pomodoro","Panino Giusto"]
columns = ["Top1", "Unaided1", "Unaided2", "Unaided3", "Unaided4"]

And a dataframe:

df=

brand          | Top1 | Unaided1 | Unaided2 | Unaided3 | Unaided4
Old Wild West  |  1   |   0      |     0    |     0    |   0
Rosso Pomodoro |  1   |   0      |     0    |     0    |   0
Panino Giusto  |  0   |   1      |     0    |     0    |   0 

I'm iterating with a for loop:

count_N= 0

for b in brand:
  b=str(b)
  print(b)
  for i in columns:
    N=len(df.loc[df[i]==b])
    count_N=count_N+N
  print(count_N)
  
  percentage_n=count_N/351
  print(percentage_n)


  print(" ")

this prints outputs like this (numbers are random):

Old Wild West
30
0.08547008547008547
 
Rosso Pomodoro
55
0.15669515669515668
 
Panino Giusto
123
0.3504273504273504

I woud like to save this output in another dataframe. The desired output is (numbers are random):

df2=

Brand          | N   | Percentage
Old Wild West  | 30  | 0.1
Rosso Pomodoro | 55  | 0.001
Panino Giusto  | 123 | 0.2

Could you help me?