Fully customized weapons would need to follow something more akin to what GCII

L did though: have pieces that all have connection points and that's where the other pieces can go. You could build off of that by having integrity points not only on the attached item but also where it was attached and the nature of the attachment. Example: anvil on a pool queue would have some difficulties with weight problems (snapping the stick because of the anvil) - but a pool queue attached to an anvil wouldn't (anvil with pool queue sticking off it) - but it wouldn't work well either.
It would be nice though if even after they were attached you could disassemble and reassemble with other things (take your anvil off and attach it to a still pole = POLE HAMMER!). You could also have different kinds of material to attach items to one another. Duct tape would be cheap, easy to find and repair but wouldn't last long and would have fewer numbers for sustaining items with higher weight #s. I suppose you could get away with allowing more duct tape to be used but that would work. Example:
Anvil weighs 40 lbs. One unit of duct tape attaches 2 lbs to an object. It will take 20 units of duct tape to attach the anvil to a steel pole. However you could use 40 units of duct tape to help sustain the attached items because duct tape has a low durability and durability is stacking (with diminishing returns). it could be made more complicated by stating that the anvil is 8 units in size and that one unit of duct tape that attaches 2 lbs only handles 1 size unit which would mean not only would it need 20 units of tape just to attach for the weight but also multiplied by 8 to handle the weight, which would be 160 units of tape (this may be more realistic but make things too complicated).
Alternatively steel bracing could be used to attach the anvil and the pole but would require the player to weld the two together - so now you've got the possibility for skill branches, higher costs, and tools required to build weapons or maybe just a smith that builds for you with higher costs, but that makes sense because you'll have a weapon with higher durability. Wouldn't want that Pole Hammer to turn into a metal staff...
Could go really crazy and have items that can be added to weapons to make them lighter, more durable, easier to wield, and increase defensive properties besides just increasing their damage properties. Those items could be real things like shoulder straps or handles, hardening sprays, plates for shielding, refining of the metal pole or items on the pole, etc.
This brings me to refinement points. Areas on the constructed weapon that could be improved by eliminating weight but sacrificing power - such as 'cutting' away parts of the anvil (rather than adding) to make the Pole Hammer easier to use. This may take away it's 'bashing' characteristics but could add 'stabbing' even tough it's still a hammer but now with a giant spike carved, chiseled, torched out of one end of it.
Built weapons could also have primary and secondary attacks. Basically you as the weapon designer decide how the character holds the weapon. Examples of how the character could hold the Pole Hammer:
1. Anvil end - not very effective if the character is holding the most damaging end, but would make the weapon easier to handle for someone not strong enough.
2. Opposite the anvil end (handle end) - can wield more damage but lack control and requires more strength and stamina to attack
3. Center of pole - holding like a staff gives player more control but less damage. Attacks are quicker but less damage.
I suppose this would get into a kind of labeling what your primary attack will be and then what secondary attack is possible in that position (or which secondary attack you'd like to be able to do). And, you should always be able to throw your weapon at the enemy, doesn't mater what it is or how you're holding it. Though the 'thrown' end should always be able to be mapped (in case you have a giant spear on the opposite end of your hammer

). Also, depending on what 'slots' on the weapon are available depends on how the weapon can be held. Holding onto the weapon's glass shard covered hammer is going to damage you every time you use it - plane and simple.
Wow, so I've gone over more than I thought I would. The Pole Hammer is only one example but i think the concept is sound enough. Anyone else have any suggestions?