Notes on this puzzle
Skyscrapers #5402 is a 7×7 city: every row and column holds the heights 1 to 7 once, and 11 of the 28 edge positions carry a clue. 7 heights are already standing inside the grid.
The left edge carries the most clues (5). 17 edge positions are blank, so parts of the grid are solved from the inside out.
Where to beginTry row 7, column 1 first: its row and column clues decide it without any other help. Use notes for the heights 6 and 7 first; once they are placed, the lower heights follow.