Multiclassing House-rule in d20

A little while ago, Roger mentioned my house-rule for multiclassing in the d20 system. Additionally, while creating Star Wars characters last night, the very situation came up. I thought I'd take a chace to explain this rule, to invite comment.

The rule comes about because of the bonuses characters get at 1st level that don't apply above that level - quadruple skill points and maximum hit points. This means that some combinations are better if the classes are acquired in one order than another. The most obvious example of this is the Rogue/Wizard.

If one takes first level as a Wizard, the character receives 4 hit points and 8 skill points. Bonuses for high ability scores apply, but are irrelevant for the purpose of this discussion. If the character then takes a level of Rogue, he gains 1d6 more hit points and a further 8 skill points, for a total of 1d6+4 (average 7.5) hit points and 16 skill points.

If one takes first level as a Rogue, the character receives 6 hit points and 32 skill points. If the character then takes a level of Wizard, he gains 1d4 more hit points and a further 2 skill points, for a total of 1d4+6 (average 8.5) hit points and 34 skill points. Clearly, the latter character is better, at least numerically.

My house rule to correct for this is that if a character picks up first level in a new class, he may gain a bonus to hit points or skill points gained to bring him into line with where he would be had he taken this class first. Naturally, this bonus only applies if moving to a class with a higher hit die and/or more skill points that the highest of the previous classes.

If a character picks up the first level of a class with a higher hit die than any of his previous classes, he gains bonus hit points equal to the difference in the die type, and rolls hit points using the lower of the two dice. A character with three (or more) classes compares the new hit die with the highest of his existing dice. Obviously, when moving to a class with a lower hit die, this rule is unnecessary.

So, a Wizard who takes a level of Rogue gains (6-4=) 2 bonus hit points, but only rolls a d4 for hit points. A Rogue/Monk who picks up a level of Barbarian gains (12-8=) 4 bonus hit points, and rolls a d8 for hit points. A Rogue who picks up a level of Wizard just rolls a d4 for hit points.

The second half of the rule applies when moving to a class with more skill points than the highest of any existing classes. Once again, it compares the new number of skill points with the highest number awarded by any existing class, and doesn't apply when moving to a class with fewer skill points than the current highest class. In this instance, the character gets the full allocation for his new level, plus 3 times the difference between the new and old allocations. These additional points must be spent immediately, and are spent as skill points for the new class. Note that no bonus is assigned for high Intelligence, since this was already received at first character level.

So, a Wizard who takes a level of Rogue gains (8 + 3*6 = ) 26 skill points. A Fighter/Ranger who picks up a level of Rogue gains (8 + 3*4 = ) 20 skill points. A Rogue who picks up a level of Wizard gains 2 skill points.

Returning to the first example above, then, the Wizard who takes a level of Rogue will have 4+2+1d4 (average 8.5) hit points, and 8+8+3*6 = 34 skill points, thus becoming equal to the Rogue who takes a level of Wizard.