Anyone know if it is possible to build a decentralised cloud storage solution on Cardano platform?
Yes. You can replicate Siacoin or Filecoin as native tokens on Cardano network. Both of those are opensource and if you are any good at converting Go or Ruby (or C) into Haskell you can pretty much copy them. Filecoin does also use Rust which is already supported in Cardano network.
In next few years Cardano and IOHK will deploy IELE which will allow you to convert most of programing languages to Cardano Network, At that point you will be able to copy almost any such project.