MS Access - Calculating Estimate Form

Hello MS Access Experts,

I designed a form for my place of business. We do estimates for roofing and construction and the form is really basic in terms of MS Access and it's potential.

But I'd like to modify it to have it make certain calculations. The way I have it setup is... on the left of the form are different fields for. Shingles, Plywood, Metal Drip Edge, so on and so forth.

This is a line pretty much of the entire form: (noted this is only what it shows)

[checkbox] Tear Off [Shingles Text Field] First Layer [# of Sqs. Field] X [FIELD = Per Square] Per Sq. = [Field = Total]

This is the way I would like to set it up.

I dont' know if the check box would complicate things but here is my idea:
If Check - # of Sqs. X Price Per Sq. = Total Price

Then I would also like to have Total Price + All Checked Total Prices = Grand Total.

I don't know if that is too complicated. I don't know anything about MS Access other than adding fields to keep data into the Database. I played with the expressions but I couldn't figure it out.