I know it's supposed to be equal to the drone's body, which is primarily determined by sized, but is it possible to increase it's strength to create a drone useful for construction without making it massive.

Funny you should ask that, because the very question (of drone Strength) came up in the game session that ended moments ago.

I just hand-waved it.

I suppose you could add cyber-arm strength enhancement to mechanical arms.

No need to suppose, that's exactly what the rules for mechanical arms state.

Thanks for the help. That's perfect.

so would the drone-strength be averaged with a base strength of body and an improved strength in the arm?
also, what about legs of walkers? can they be enhanced like cyber-legs too?

if all else fails, you can always just put in the special machinery mod or whatever it's called. just declare that the attachment gives the drone X strength for the purposes of lifting, assign it a price, and you're good to go.