Add sugar slowly dissolving as you go, stop when it won't dissolve any more.

That will give you thick syrup. The exact ratio is not critical.

I would caution regarding mixing large batches as it is susceptible to fermentation.

Fred Dunn says you can add a touch of bleach to it to prevent fermentation. I don't recall the ratio, check his video. Anyway its a very small amount, liken it to chlorinated city water. You will often see bees drinking out of a pool..... Essential oils will also prevent fermentation, but I'm not sure they are appropriate for this time of year.