For simple decks, you might want to look at these by elvenor:
<kuid2:63290:26023:1> House porch for brown
<kuid2:63290:26016:1> House porch small
The porch for brown is a full deal with a roof sort of like a farmer's porch. They're meant for a series of simple white houses he made without a lot of details. I have used them as add-ons for other houses.
The House porch small is a small back stoop like deck. I'm not sure if it's useful, but it might be if you want to put two down facing each other to make the small stoop bigger.
Advance made a few decks. They are a simple plain without any other details so I'm not sure how useful they might be.
<kuid2:102657:25038:1> Wood deck 12 x 12
<kuid2:102657:25036:1> Wood deck 16 x 12
<kuid2:102657:25037:1> Wood deck 16 x 16
<kuid2:102657:25041:1> Wood deck 21 x 12