Some people would encourage you to use D20Mecha as it's apparently more balanced. I have no experience with it, though, so I can't really comment on it.
I don't really know how the mech rules work in D20 future because I haven't ever run them.
Allow me to explain:
Because the mechs of the Battletech universe are so large, they all would fall under the Gargantuan and Colossal size categories. d20 Future will not work for what you want. At all. The scaling between HP, hardness, and damage in d20 future's mecha rules is so poor, its completely useless for making mechs bigger than Large.
@narukagami how do you think houseruling different parameters for the sizes would work? Is that the main problem?
Does it focus more on the anime-esque mechs or the walking tank style?
Neither and both at the same time. Its whichever style you want it to be.
At its core its just construction rules to be used with any d20-based game. What I, personally, like the most about it is how its very easily configured to work with the vehicle rules of the core Modern rulebook.
The link to the rules are in my sig, by the way. The d20 Mecha SRD is free.
@narukagami how do you think houseruling different parameters for the sizes would work? Is that the main problem?
The main problem with weapons is that hardness and HP scale with size. Weapons don't. So with Battletech size mechs you'll have the problem of mechs with 20-30 hardness and 300-400hp getting shot with weapons that do small dice pools of damage. So you end up with single combat encounters that will literally take hours because mechs are completely incapable of doing anything but scratching each other unless they roll criticals.
This is ignoring all the other problems with the d20 Future rules. Like how its virtually impossible to have anything but a mech vs mech battle because of how vastly different all the rules are for various vehicle types (another problem d20 Mecha fixes, by having ALL vehicles follow the SAME rules).
The only downsides to d20 Mecha are that
1) Since its mostly a construction set, so you have to do all the work and statting yourself, and
2) It requires some degree of common sense to keep the things you stat with it from getting absurd or broken. My recommendation is to use the system to stat everything yourself beforehand (essentially make your own mechs and weapons lists) and not allow the players to build their own mechs and weapons from scratch, or at least not without your input.
@ master vega: thanks for the heads up on d20 mecha I'll have to check that out. Does it focus more on the anime-esque mechs or the walking tank style?
@narukagami how do you think houseruling different parameters for the sizes would work? Is that the main problem?
I'm not Master Vega or Narukagami, but from what I have read in the D20Mecha SRD, it seems like you can use the rules to create any thing from a skateboard to a star destroyer; including weapons.
As for house ruling D20 Future, what I do is give all mecha weapons a x4 multiplier to range and damage, and I give all starship weapons a x10 multiplier to the same. It makes them a bit more useful.
you could also increase the die type depending on the size of the weapon, or increase the crit range by one for every size category above large...
I know I might come off sounding like a cheerleader for D20 Future. Believe me I'm not... but I used to spend a lot of time trying to "fix" it, so I've got a binder full of house rules that I am more comfortable with than using some other system.
Anyway, good luck!
