Create Item Availability Views - Date Calculations

I am having a hard time creating a view with some complex math to chow availability for rental items.
My tables are as follows:

OrderHeader

OrderID int,
Site int,
StartDate datetime,
EndDate datetime

OrderDetail

OrderDetailID int,
Site int,
OrderID int,
ItemName varchar(30),
Qty int

ShipHeader

ShippingID int,
Type int,
ActionDate datetime

ShipDetail

ShipDetailID int ,
ShippingID int,
OrderDetailID int,
Qty int

Transaction

TransactionID int,
Type int

PurchaseHeader

PurchaseHeaderID int,
Site int
PickupDate datetime,
ReturnDate datetime,

PurchaseDetails

PurchaseDetailsID int,
PurchaseHeaderID int,
ItemName varchar(30),
Qty int


I need a view that shows how many items will be available on a particular day for a specified item, date range and a specified €œSite€? (Office location. For example, NY, LA, CA, etc.)

The quantity actually owned is calculated from the Transaction table. Type, Qty are the columns. (type 1 is a purchase or addition and type 2 is a sale or subtraction. The quantity owned is the sum of all type 1s minus the sum of all type 2s.

The ShipHeader table also shows types. Type 1 is ship, Type 2 is return and Type 3 is lost.

Initially, all availability is calculated based on the FromDate and ToDate of our order headers. However, once the order has shipped, the availability should change to our ship and return dates in our ShipDetails table. Additionally, there is a PurchaseDetails table that shows items to be €œSub-Rented€? for a time frame. The PurchaseHeader table contains the FromDate and ToDate for these sub-rented items to be added to availability. If an item is kept beyond the due date set in the OrderHeader, then the item should show as unavailable from the FromDate through all future dates (as there is no way of telling when a late item will be returning. Once, the item is either returned or marked as lost, it should become available again as of that date.

The view should list dates in each row with the number of units available on that date.

Also, a second view needs to be created that shows the details for the dates listed in the first view. this is essentially a list of the orders or puchase orders that were used to calculate the number available.

I think this covers it.

As I said, this is a bit complicated. i understand what needs to be done but need assistance assembling the code to make it happen.