Don't pay anything extra on that loan and don't pay anything extra to the builder. If you have extra, hold onto it as long as possible because you will need it for overages or for unexpected expenses throughout your build.

Thank you JDez.

Anybody else out there that has done something different?

Think about it this way. Your interim loan is for a specific amount. If you spend your extra money paying it down, you have technically already spent a portion of it. It is not what the call a revolving loan (like a credit card). If you have the loan for 100K, spend 20K, pay 10K on the loan, you have 80K left to disperse.....even though you now owe 10K (plus interest).
The reason you don't pay extra to the builder is the same reason some millionaires choose to have a bank finance the build....to protect yourself. Assuming you need the loan when the house is built, you are also going to have to show the money you have put into the loan equals "x" percentage...this becomes more difficult when you are giving random sums to the builder.
Paying interest sucks, but the 12 months during the build is not where it adds up, it is the 30 years it takes to pay off the mortgage. Save the extra money at the end of the build for a hefty emergency fund, then start paying down the mortgage so you have it paid off in 10-15 years...this will save you the most interest.
Sure, there are many others who have done it differently. You can do it however you want, as long as the bank will let you.

I took out a construction mortgage through the bank. Anything put towards the house counted as down payment, so I paid the initial deposit to the builder to start. The builder had an option that if I bought the land (that they owned), they would take 1% off their management fee (which was 15%). So I did. All of that, again, is down payment to the bank I would have had to pay anyways, so it made sense for me to save the 1% in fees. The rest will be through draws.

I agree with previous posters that I would try to minimize the amount you paid to the builder as much as possible and let the bank handle the draws. I'd put down lump sums back to the bank only once the construction is completed and you're happy with the build.

Thank you so much for the info!!
It has been very helpful, and informative.