Daron Williams wrote:Hello and welcome to the forums!
Starting construction now should not be an issue overall but here are some tips that I think would work better than placing a tarp over it all.
I would build it now with the soil and spread a cover crop over it. I would go with a cover crop that would not over winter - a mix of plants could work well but I would focus on nitrogen fixers. Once the frost hits and kills off the cover crop I would add a mulch layer over the top. Something like wood chips or fall leaves. The cover crop and the mulch will keep the soil surface from being exposed which will protect it and unlike a tarp it will improve the soil and help get you off to a good start for your spring planting.
Depending on your weather right now you may need to water the cover crop until it comes up and gets going.
Hope that helps and I'm sure others on here can provide some advice and more information on cover crops.