need advices : materials manager database design

I need to build a intranet website which will manage all materials (computers, cars, printers, ...) for all centers of my company. I will build it in c# but I'm very bad in architecture design. Can somebody help me to define the database ?

Each material can be affected to a center, a user or to the company (like servers). This application have to allow some actions to users, depending on their rights, which I define here :

- A simple user can see material affectations for his center.

- center's manager can see affectations for his center or the centers of his region, can ask new affectations for a material and can modify his center's materials.

- director or comptability can consult every centers, apply new affectations, modify the application (add/modify/remove : materials/people/centers/regions) and can see the financial stuff for a material/center/region (like the prices, financing companies).

- the application manager (me) can consult every centers but cannot modify anything (should be at least).

In addition to that, I need to store materials informations from the technical stuff to the financial.

If anybody can give me some advices, it would be really helpful !
I can also post the file containing this project specifications made by my employer if anybody accept to spare a bit of time to help me

All the code I will write and all the project preparation (UML and database design ...) will be posted here once finished so if anybody need that kind of applications, I hope to save some time !

Thanx a lot !

These are the tables I think to add, please correct me if I'm wrong :

Users
- Id
- Username
- Password
- CenterId
- JobId

Centers
- Id
- DirectorId (a user)
- RegionId
- CompanyName

Regions
- Id
- Name
- Description
- Director (a user)

Suppliers (and the same for Constructors and FinancingCompanies : maybe in this table also ?)
- Id
- Name
- Address
- PostalCode
- City
- Phone
- Fax

Materials
- Id
- Designation
- Brand (HP, Chrysler, ...)
- Modele
- ConstructorId
- ConstructorReference
- SerialNumber
- SupplierId
- DeliveringDate
- DeliveringReference
- GuarantyLength
- BillReference
- FinancingCompanyId
- FinancingReference
- UnitPrice
- Notes
- CurrentAffectation (? not sure at all as it could be a user, a center, a region or the company itself)

UsersRights
- UserId
- CenterConsultation (Yes/no)
- RegionConsultation
- AllConsultation
- CenterAskAffectation
- RegionAskAffectation
- AllAskAffectation
- CenterAffectation
- RegionAffectation
- AllAffectation
- CenterModification
- RegionModification
- AllModification

That's it ! I'm sure I make a lot of mistakes as I'm not a database designer so if anybody can help...

Thanks again !