Design and build according to Macro Principle No1.
1.It is ugly but
it works
This practical transporter prototype works from me already 4 years like a dream,
replacing wheel barrow most of the time and saving a lot o effort in our hot climate.
Can carry up to 350kg (or more depending on wheel quality) uphill , downhill or in rough terrain.

Could carry bulk material or long stuff. converted in seconds
Low center of gravity provide ultimate stability and minimal effort to load/ unload or even tip.

Powered by 1000 W DC electric motor ( from discarded wheelchair)
Powered by 20 Ah 36V Lithium battery for electric bikes. Rechargeable in couple hours.
One charge last for few days work.

Speed controller from 0 to 8 km/h
and reverse switch.
Reverse useful for braking down hill -as mechanical brakes inbuild but sill not yet connected to handle bar.

I wish we could walk to Bunnings to buy one of those , ready for work of the shelve.
Cost of all material used below $500
Main idea here is universal moving platform. Dependable, expandable and strong.
Ideally, commercial version should be powered by 4 in wheel hub motors ( geared and with inbuild brakes) , for simplicity of construction.