Eddy is right in the foreach, but for recalculation, I'd have a handler that handles the on change event from each of the boxes, it can all be done in one subroutine

'kinda like this
private sub TextboxChanged(sender as object, e as eventargs) handles txtRoomWidth.changed, txtRoomLength.changed, lstFlooringType.changed

dim SquareFootage as single = txtRoomWidth.value * txtRoomLength.value
dim CostPerFoot as single 'Insert code here to get the cost per square foot of the current flooring type

dim RoomCost as single = Squarefootage * CostPerFoot

'put code here to insert the cost into the list of costs

dim totalprice as single = 0

foreach RoomPrice as single in RoomPriceList
    totalprice += RoomPrice
next

txtTotalprice.value = "Total cost is $" & totalprice

end sub

I'd have used the names you used, but I can't open both windows at once

OK, from a relative novice, here's the way I see it, and pardon me, but I come from a Qbasic/VB background. As for multiple returns, if you have 10 conditions, lets say in a "Select case" statement, I see it OK to use multiple returns... if you have returns scattered, then I can see a problem. I find the following a neat way of doing this... I'm usually not much for the ":", but again I find that on something simple like this, putting the condition and the return value on the same line improves readability

Select case i
case 1 : return false
case 2 : return true
case 3 : return false
end select