I need to make this for the top of a cake for this Sunday.

What does everyone think would be the best to use? Gumpaste? Fondant/Gumpaste? Colorflow? Iced Cookie?...And It has to stand up...

I would be inclined to use color flow, with a good application on the back to encase a couple of skewers for support. (Or in the case of some I've done, a couple of popsicle sticks.)

These figures were color flow:

<a href="http://cakecentral.com/g/i/1475187/a/1476187/a-favorite-t-v-program-brought-to-cake-i-drew-the-characters-then-filled-in-with-flood-work-rocket-ship-is-cherry-flavored-fondant-covered-cake-rocket-rear-is-gum-paste-while-the-rockets-are-fondant-covered-rkt/"><img src="http://cakecentral.com/image/id/862944/width/400/flags/LL"></a>

As were these:

<a href="http://cakecentral.com/g/i/2184394/a/2185394/for-a-one-year-old-who-loves-word-world-the-cake-and-the-smash-cake-are-wasc-strawberry-bc-filling-white-choc-cheesecake-mff-over-white-choc-ganache-figures-are-flowed-sugar/"><img src="http://cakecentral.com/image/id/233805/width/400/flags/LL"></a>

Jan

I was leaning toward color flow as well. The party is Sunday at 1:30. I won't have time to do the piece til Wednesday night. Do you think that will be long enough for the piece to dry?

And when do you put the skewers on?

AI would make the color flow piece, set overnight or however long it will need to dry completely. Then turn it over, attach your supports & let dry completely again. I'm not sure if it works this way, but I might try to strengthen the whole piece with a thin layer all over the back when you place your supports.

Do you use colorflow on the back to attach your supports as well?

I place my supports on the backside of the dry piece and paint the color flo over the top. This strengthens the piece and also embeds the support.

Jan

I'd do it in gum paste or fondant with tylose/cmc/gum-tex added to it.

I'd make a single backing piece the size of the entire piece, build up the features, having inserted 3 skewers into the thicker part--the facade with the door and window--one dead center and one at each inset corner. 

I'd dry it flat in my oven with just the light on until Saturday and then I'd continue the drying process using a fan, turning it over every now and then, until the time that I packed it up in an unsealed cardboard box for delivery.