While not wanting to disagree with TGH or CG, their experience is much greater than mine I would look at it a little differently.
I would not go for dwc or rdwc, I would look at either ebb & flow or NFT. Both these systems need much less water, though a large flowering plant can drink 10l per day! Have you thought how you will get that amount of water into your attic?
Your space may be 10 x 10 but have you thought about making the grow area smaller?
Why do you want around 15 plants? DO you have a medical need for your meds? If so, how much do you need? Could you get the amount you need from fewer plants?
As the guys said, controlling temps in your attic will be your biggest problem. Where in the country are you? I am in the Uk and loft insulation here is a big thing, my loft is ALWAYS freezing, around 10deg lower than the house which is different to the guys speaking here.
If you work backwards, starting with how much weed you need, then work out how many plants you need to give you that, then how much space is needed, then how much light is needed. I believe what you are wanting to do is possible with a lot of thought and planning.
Access, water and temps will be your biggest barriers to success but ultimately they can be overcome.