With any building layout, I prefer having more entrances/exits. Multiple doorways and stairwells makes gameplay more interesting. Would be nice to have well lit buildings too (with artificial lighting if possible). Recreating MOUT would be pretty sweet.
In general cover, lots and lots of cover. Be it old cars, barrels, anything that can act as cover.
Lastly I think wouldn't mind a bit of (see below) on the field
... please and thanks.