growing attic

You have a few choices as per wall cover.
For the best results, it should be white, but reflective is good too.
In a small area, I have tried mirror with great results.
When the room got bigger, I tried the shiny foil paper with a paper backing, that they use in construction as a a heat reflector inside the wall between the wallboard and the framing.
This worked well and it was easy to install since it comes on rolls of about 4' wide.
You might have to buy a full roll and that is where it could get expensive since you only need a few feet and it comes in like 500' rolls.
Even then, a big roll is only about 20 or 30 bucks and it will do the job.
You can put it up in seconds with an exacto knife and a stapeler.
Like I said though, white is better, but I had this lying around after a renovation project and I got curious.
As for even buds, you could try tube florescent on the walls in a vertical installation, but it depends on how close the walls are to the plants.
Too far and they are not effective.
Space is the key due top the heat factor.
The bigger the space, the further away the walls end up from the grow, the smaller the room, the more ventilation you need.
It's a trade off.
You should be ok with just thew top lights though, since the buds tend to find the light themselves.