Sum Skyscraper puzzles are a variant of Skyscraper puzzles. They use similar rules, with Sudoku-esque square grid and exterior 'skyscraper' clues, but unlike in regular Skyscraper puzzles the clues represent sums of visible numbers rather than observation counts.
Specifically, each digit placed in the grid can be imagined as a building of that many storeys, so for example a '3' would be a 3-storey building. Next, each given number outside the grid reveals the sum of the number of 'buildings' that can be seen from that point, looking along the adjacent row or column. Every building blocks the view of all buildings of a lower height from view, while taller buildings are still visible beyond it.
For example, if you look along a row and see "1 2 3 4 5" then the clue at the start of the row would be 15, since no building obscures any other and the sum of those buildings is 15. If instead you looked along and saw "1 4 2 5 3" then the clue would be 10, since three buildings can be seen (1, 4 and 5, whose sum is 10).
Every puzzle has a unique solution that can be reached using only reasonable logical deduction. If you're a Sudoku expert you'll definitely find that some of your skills come in handy with Skyscraper too!