A while ago, I did a rough calculation that we could create floating islands from tying plastic bottles together. My calculation accounted for enough dirt for trees (several meters of dirt) and enough land to grow vegetables and such.

Accounting for food and housing needs, it was like 10k people from Europe's plastic bottle waste for a year.

Personally, I think something like Netherlands dikes would work in many places.

Not sure how to deal with the heat though. Unfortunately heat is thermodynamically useless without a sink. Space is a bad sink. Deep ocean maybe.