Notes on this puzzle
12 clues around the edge, out of a possible 16, frame this 4×4 grid. 2 heights are already standing inside the grid.
There are 4 clues of 1 around the frame; the first cell beside each of them must hold a 4. On 1 line the two opposite clues add up to 5, which fixes exactly where the tallest building stands. The top edge carries the most clues (3). 4 edge positions are blank, so parts of the grid are solved from the inside out.
Where to beginTry row 3, column 4 first: its row and column clues decide it without any other help. Place the 4s next to every clue of 1, then fill each line like a tiny sudoku.