Im gonna try to get my idea out as simple and quick as possible.
One of the main problems in the beta atm is rook, The problem with the rook is that most of his damage comes from his abilities(A certain 2.1k hammer comes into mind). As such he has no real need to go for items that improve his attackspeed or damage with normal attacks, He can get an mana item or so and then go with Health items for all slots that are left. This means the Rook get almost indestructible lategame.
If you take a look at this graph quickly.

What you see that not only do the rook start the game of with about 500 hp more (125%) but he also ends the game at lv20 with close to 2000 more in health. My hopes for the next beta is that his starting hp and growth gets nerfed but we will see for how much.
So anyway this base growth in HP as well as the rooks option to go for almost only HP items means a rook with 8k+ hp is really not such a rare sight, these rocks often walk around on the same battlefields as 4k Erebus and Regulus, which should give you some perspective.
So due to these effects, Im eager to present a function which I would like to say is a way to force the rook into buying some weapon damage to actually deal damage. The concept is quite old and its been used in alot of wc3 RPGs including my own, The Kingdom of Kaliron (TKoK). It works as such
Skill:Hammer slam Lv1
Casttime:1 sec
Manacost: 360
Description: The Rook slams his hammer, dealing [3*BaseDamage] damage in a small radius and [1.5*BaseDamage] damage in a larger radius.',
This skillsystem uses your current stats to determine the damage of the spell, The positives are that the abilities using this function all becomes scalable over the whole game, It doesnt limit you to the damage the ability is set to but you are actually able to sa:
"Hey, my hammer slam isnt really doing too much damage. Perhaps I should get some more weapon damage to help me take down that tank specced UB"
To get a clearer view about how this would effect the rooks gameplay we can take a look at his damage in another of my graphs.

We see the rook starts off with about 180 dmg, If he decided to go with hammer slam as first skill the hammerslam(using my example values) would deal a total of 180*3=540 dmg.(Beta 3B Lv1 damage is 500dmg). So it would be quite equal to what it is now, However!. The rook may decide he is going to go a damage build, as such he starts the game off by buying the +25 dmg gloves, knowing it will improve his hammerslam to deal (180+25)*3=615 dmg.
Not only does this make playing the Rook much more fun, it gives the rook a real reason to get some weapon damage and not just health items.
Also if this system was implemented it wouldnt have to stop with just rooks hammer, Imagine regulus snipe dealing damage based off his bow damage for example. Or to be really out there, The Torchbearers fireball dealing fireball damage equal to 350 + [totalmana/100.
I should probably quit this thread now, I wrote it in order to bring this idea back? to the developers. And I do understand that this change would be a too big one to get into the release version. But Im hoping that it still could be something worth spending time on for one of the DLC packages not too long after release.