As you know a lot of Online-Games have this function, so here my ideas for CoC:
1. How to purchuase?
- "Boost" the TH with gems
- Direct with real money like gems
2. What does CoC premium?
- Always +20% troop and spell building time (extra 2h boost possible)
- +20% war bonus
- "Golden hammer" - a tool you can give one builder to decrease the building time (maybe 20%?)
3. price / duration
- 4 weeks / 500 gems (?)
more suggestions and constuctive critic are welcome :)

