Hello,

Such platforms cost tens of millions to build, maintain and especially advertise. Even i you build one, the marketing budget should be quite high.

You also need something to differentiate them, like for example Clarity is different from Upwork due to consulting focus.

If you still want to do this. start doing some specs, have them reviewed by a system architect to chose a technology that fits and to estimate the development hours than put together a team and build it

Please let me know if you need any help, .i have a solid experience in building platforms from scratch.

Thanks,

Seb