Roasted a portion to see the difference.
300g before roasting, 270 after roasting, 42 kcal in difference.
42kcal isnt that much, but it is a little.

Should i weigh before or after roasting them?

Even if the nutritionalmass goes up (More nutrition in less space, because of roastion), it would still weigh the same way, right?

the 30g's thats disappearing is probably water.