I was wondering how long the side effect of roost lasted, you know, where you temperarily lose your flying type. Does it last for the match, until you switch, for an X number of turns etc.? I was wondering if I should use it instead of rest on my skarmory, but if it lasted for the match my poor silver chicken would be weak to EQ.

Not sure about it's expiration .....

But you said WEAK AGAINST EQ ?
I tought Skarmorys was supposed to be a Physical wall ?

In my somewhat limited experience, Roost lasts until the end of the turn in which it was used.

Just clearing amattson7919 ,

we are talking about the loss of it's Flying-type !!!

IIRC, it only lasts till the end of the turn.

About whether you should have it on Skarm - true, it would be weak to EQ, but then it would lose its weakness to Electric attacks. (And what opponent would attack Skarm with phys EQ when they could attack with a possibly special Fire or Electric? But Fire Blast is more common than Thunder cause of the acc...your choice). Also, Rest removes status, which Roost fails to do.

The loss of it's flying type from Roost, right?
In my experience, that lasts until the end of the turn in which Roost was used. I've tried to take advantage of the loss of flying type to hit things with Earthquake in the following turn, but things were always flying again.

Oh, so since skarmory usually goes last anyway, the side effect of Roost is basically negated? So it would be like the following:

Salamence used Dragon Claw!
Does something damage
Skarmory used Roost!
Skarmory recovered 50%, Skarmory lost its flying type!
Skarmory regains his flight!
End Turn

So the above should be correct? (I made it up so its not word for word)

I don't know. Somebody should do a test on that.

that's the question isn't it? Whether it loses its flying type only that turn, or if it continues until it attacks again?

(I know it doesn't last until you switch/faint)

without a doubt, this is true. my friends skarmory used roost, and i told my dugtrio to use earthquake on the next turn, but i got the usual "it doesnt effect the foes skarmory" message. so yes, on a slow pokemon its as good as recover.

now, i wonder what would happen if mew used it? it doesnt have a flying type to lose. i guess it would be the same as softboiled?

amattson's right. it only lasts until the turn it used. It is somewhat useful in most cases. That is if you go first.