Rules Cyclopedia: Falling Damage and falling objects

When a character falls, they take 1d6 damage per ten feet fallen (to a limit of 20d6). This is irrespective of the mass of the character. Now if a character weighing 200lb falls ten feet and takes 1d6 damage then they have been subject to the damage inflicted by a 200lb falling object. A two hundred pound object falling ten feet from the ceiling exerts the same damage to the character that the two hundred pound character would experience making the same fall.
If a two hundred pound object inflicts 1d6 to a two hundred pound character over a distance of ten feet, a two hundred pound object inflicts 2d6 damage to a one hundred pound character simply because this is double the impact mass of the one hundred pound character.

The effect of impacts by Stone Bricks of various weights
Weight (Size)                                         Damage per 10ft
Character weight:               75lb        100lb     150lb    200lb       250lb
1lb (0.00587 cubic feet)      1hp         1hp         1hp       1hp           1hp
170.24lb (1 cubic feet)        3d6          2d6         2d6       1d6           1d6
1 ton (13.15 cubic feet)     20d6       20d6        15d6     12d6          9d6
76 tons (1K cubic feet)      20d6       20d6         20d6     20d6         20d6

This of course does not factor in continuous crush damage. Let's call that 1hp per round per multiple of PC weight. This is useful because armour weight effectively helps reduces the damage taken from the initial impact, and from subsequent crush damage.

Example: Fared the 9th level Sworder (44hp) is crushed under a one ton block dropping from the ten foot high ceiling. He takes 9d6 (28hp) from the initial rock fall, but after that the 250lb warrior takes (2240lb ÷ 250lb=8.96hp) 8hp per round until he dies three rounds later (44hp)-28hp, (16hp)-8hp, (8hp)-8hp. His Companion Mirandar the Elf has one round to get the rock off his fellow adventurer before Fared is crushed to death.
Alternatly Mirandar the 75lb 9th level Elf (40hp) sees the rock falling and knocks Fared forward taking 20d6 (67hp) damage which kills him instantly.

Effect of Arm. Wt. on damage from 2,240lb block falling 10ft

                                                       Unarmoured weight

Armour             Arm. Wt.   75lb   100lb     150lb      200lb    250lb

Unarmoured          0lb        20d6  20d6      15d6        12d6      9d6

Shield                       10lb     20d6  20d6       -1d6        -2d6      -1d6

Leather                    20lb     20d6   -2d6       -2d6        -2d6      -1d6

Scale Mail                30lb     20d6  -3d6        -3d6        -3d6      -1d6

Chain Mail              40lb     -1d6    -4d6       -4d6        -3d6       -2d6

Banded Mail           45lb     -2d6   -5d6        -4d6        -3d6       -2d6

Plate Mail                50lb     -3d6    -5d6       -4d6        -4d6       -2d6

Suit Armor              75lb     -6d6    -8d6       -6d6        -4d6       -3d6

As you can see, armour contributes some protection from the impact of a falling object though heavy armor contributes its best protection to those of 100lb weight. Those with greater or lesser weight recieve less benefit from heavy armour.