some_dict=defaultdict(dict)
for x, y, z in zip(val_df['timestamp'].values, val_df['res'], val_df['building_id']):
    some_dict[z][x] = y

new_col_plus = [some_dict[row['building_id']].get(row['timestamp']+np.timedelta(1, 'W'), np.nan) for (ind, row) in val_df.iterrows()]