Steve's Blinds online FOR SURE. Can't recommend them enough! Done this in a lot of windows. Roll shades and Roman Shades in gorgeous fabric. Order sample fabrics. DIY measure, order, install. Or they can install. They look beautiful, fit nicely, great sturdy materials, construction, and a SUPER value.

Even got some long pull chain ones for our celestory window because we didn't want another remote to lose lol. Super easy to pull up and down. We had those installed by our handyman, no more ladders lol. Yes we had some 70 inch windows too.

Pottery Barn offers some semi custom Roman shades options. You can choose the width but the lengths come in preset values…and I’m pretty sure 70” is one of them. Not a ton of color options, but the cordless mechanism works well and no parts seem flimsy. Attaching the word custom to anything increases the price automatically but PB has plenty of sales that help offset it.

I've used Steves for years and you just order what you need in all meausrements. They will send samples too.