Hello there, @JamesCrozier.

Allow me to share additional information on how you can maximize the use of your QuickBooks Online account in adding mark up to your estimates.

I understand how important it is for you and your business the ability to add mark-up on estimate in QuickBooks Online. I'd personally share this to our Product Developers for consideration in future product updates.

While this feature is specifically for billable expenses on the vendor side, you can utilize the Bundle feature to enable markups on estimates. You just need to add the mark up as a service or product item. 

• There is a limit of 50 component items in a bundle which is convenient for your construction business.
• If you already created a bundle, you cannot bundle another bundle.
• You cannot assign bundle to a category, however you can sort out your inventory by Type.
• When converting an estimate to a purchase order, the bundle will not transfer but its parts can if the purchases description and cost have been filled in.
• For individual entry, you can add the Mark-up item as a line item to Estimates, Invoices or Sales Receipts.
• Bundle can used in creating: Estimates, Invoices, Sales Receipts, Credit Memos, Refund Receipts, Delayed Credits, and Delayed Charges.

First, let's create a service item for the mark-up:

1. Go to the Gear Icon.
2. Choose Product and Services.
3. Click New.
4. Choose Service.
5. Fill in the item details.
6. Make sure to choose Mark up as the accounts affected.
7. Click Save and Close.

To create a bundle, here's how:

1. Click Gear Icon.
2. Choose Product and Services.
3. Go to New button.
4. Select Bundle.
5. Fill in the Bundle details.
6. Add the products and services included on the bundle.
7. Click Save and Close.

Once completed, you can now add the bundle on the Estimate you are creating. Here's how:

1. Click the Plus Icon.
2. Choose Estimate.
3. Complete the Estimate detail.
4. Add the bundle you've created, look for the name of it from the Product/Service column.
5. Click Save and Close.

You also have the ability to choose whether you want the components of the bundle to be included in printing and sending the estimate. Just mark indicate in creating the Bundle item.

With our goal is to make QuickBooks as user friendly as possible for all the small business owners, so feel free to share with us if you have suggestions for improvement.

That's it! This should get you on the right track in  adding mark-ups to your estimates.