Andor's Trail

I just have to point out that a shield worn in two hands would be more difficult that wielding it in one arm, as it would require one to actually use one's hands - making it heavier. Traditionally, you rest the weight of a shield on your shoulder, making even the heaviest of shields rather easy to bear. Actually having to carry it in your hands would place the weight too far out and make it completely unbalanced and exhausting even to swing.
It is a nice thought, but I'm afraid that the concept is highly fallible.
The only two-handed shield is used in barricades, supported by your weight (like a small wall), where you never have to move as it would take way too much effort to actively handle. These shield are dropped in the event of the enemy breaching the line.

So, I would definitely not make a two-handed shield constructed in offensive purposes. It would be way more efficient, no matter the weight, in one arm.
Though it may be exhausting, you can wield a shield up to 5 kg in one arm in active combat. However, I would not recommend carrying it more than an hour. It may not sound like much, but,trust me, a 2 kg shield is by far exhausting enough, no matter your muscle mass.

Back to the point: a 2h shield is not recommended.

actully I would like to have two handed long and big shield with spikes and a flattened base so whenever in combat I can plant the the base somewhat into the ground and fastly moving only its upper part while the base remains stationary. and as the shield is long enough I can hide myself completely behind the shield and attack the enemy while defending myself at the same time. also the shield have spikes so if an enemy tries to attack me hard he also got some damage. I hope you can imagine what I want to say.

edit: the only problem will be to drag the shield around and if you are taking rest some spikes may poke .

A shield that would stand balanced on the ground whilst having its upper part maneuvered would only add to defense, and would probably lower your damage. Thorned or not. (Thorns would merely deter an enemy.)
Attacking with suck a construct would not be effective at all, when taking into account the lack of kinetic energy you can conjure through such a maneuver.
The case would be the same as when handling an ordinary two-handed shield; in close combat you would not stand the hint of a chance. You would have to drop it in order to actively fight back.
If if were, as you suggest, stuck into the ground as well, if would be even easier for the enemy to come around it. In your best-case scenario, you both would just run around the centre of the shield, chasing one another endlessly.

Two-handed shield are used in battle formations only, with spears backing them up. In solo fights, they are utterly and completely useless.
Pardon my being blunt ^^

lunatic you got some better points but this is a game not real life so atleast we can have some fantasy weapons or shields at some points.
and these forums are meant to discuss so go on dicussing.
and I like the point of endlessly running then at somepoint when the enemy is tired we push the shield over the enemy and he will be trapped under it for sometime then comes the time to draw a fastmovin dagger:D.

But this game is (somewhat) within the frames of realism as it focuses on balance and what would be physically possible, and that is why I'm quite relentless (a paradoxal statement, yes) regarding the actual use of such an item
I am discussing, and my argument is highlighting the cons of having the said items as two-handed.

Drawing the dagger would still make the shield one-handed, as you would have to wield the dagger (in-game) as you stab your enemy trapped under the shield

yeah, then I'm fine with my dagger and one handed shield .
but then I am thinking that rijackson741 is also working on a shield that reflects the enemy's image so if he can also implement a thorn in it then the enemy can get some backdamage which makes the shield really legendry .

That would be neat!
Combine the two shields to make the ultimate deterrent for any and all foes! How could one not fear a spiked mirroring shield that peirces the inner essence of your very soul? ;D

And make it convex so that enemies see themselves fatter than they are, get depressed, and commit suicide by letting you kill them...

I must be tired. ....

New actor condition: "Depression". AC -10, BC -10, Move cost +2, Attack cost +1
"Shield of Despair": Stats TBD, on hit, on target, 30% chance of Depression, 2 rounds.

Depressive monsters - that is good!
But why not? And a maybe 5% chance of suicide?
Great idea!