Home DIY

Can't do CAD so had to use Paint, but I think this is the most efficient.

Do column a and b as normal. Split column c in half at the edge of wall 1. Use the second half of column c and column d to do wall 2. (Note, there's not a massive amount of wiggle room here; total width of the two walls is 205cm and 4 rolls of wallpaper is 212cm). So essentially box 1 goes onto wall 2. So you don't need column e there.

For walls 3/4, alternately split the rolls so that you have 6.something squares for column f, then 4.something for column k, then 6.something for column g, then 4.something for column l, etc. That means you can lose the bottom 5 squares on wall 4 and move box 2 to the top of wall 4. Also, use the remaining bit of column j to replace column o.

That would in total save 14 squares, bringing the total down to 71. Which means it's possible to do it with 4 rolls, even if you account for the fact that a roll is just slightly short of 19 squares.

You'd be pushing it in terms of room for mistakes I think though.