Any mechanical engineers here who can answer a few questions?

Trying to think about how the lowest common denominator's problems can be solved.

Major issues that still persist in slums -

Housing and rehabilitation Plumbing Toilets Water access

Could there be modular houses built/assembled in a day or two out of cheaper and lighter materials that are more durable than mud/dirt? Shipping Container houses being laid down using a crane was my initial thought, but cranes are hard to fit inside narrow lanes, so assembly might be better option.

Instead of constructing a complete cement and brick building somewhere, maybe some Lego housing would be easier. Might be possible to stack upto 2-3 floors. Maybe a porta-potty optional variant where plumbing for toilets isn't available. Rainwater harvesting and solar panels built on the roof maybe. Sink water should collect for use in toilet flush like it happens in Japan.

Apart from housing, for employment I was thinking about upgrading the hand cart that Indian hawkers use for selling veggies , street food etc. They are a pain to move around and use because they're bulky.

Features I'm thinking about adding -

2 floors of the cart, one where motor is kept (with storage area next to it) and second where stuff to sell can be displayed above the motor floor (some hand carts already come with a lower section but it is usually open). Covered on all 4 sides.

Once work is done, stuff can be stored inside the storage area on the motor floor, while owner can sleep above it. Convenient for those living away from home. Locking it up from inside instead of outside when sleeping in the cart, like an airplane lavatory lock. One seat in front of the cart with a steering wheel.

On the roof - solar panels that can charge a battery to operate a small fan, LED lighting & a charging port/plug for phones and small devices. Not sure if the panel can power the motor for a large cart, maybe electric motor if it can. Otherwise petrol/diesel motor.

Thoughts?