Custom checkout/order & payment process (pos thro wordpress)

I'm looking for someone to set up a checkout/payment page for a pre build roofing dormer company of ours. To explain a bit, there will be two options presented to the user on the order page: * Pre-build dormers * Custom dormers The pre build dormers with have a selection of drop downs (height, width & pitch) for the customer to select. This would look through a chart to determine a price and output this to the customer. They would then move onto name, address, delivery etc etc. And then payment methods The custom dormer option would be a call to quote type option. They would simply be text fields for (height, width & pitch) with a continue button onto name & address. Then someone our end would get back to them via email/phone for a price. For both options there will need to be check box for add-ons like cladded cheeks & plastic add-ons amongst other things. These would be set prices and would simply be added onto the grand total. The site currently is built on wordpress, i'm not sure how easy it'll be to tie it into it but this is not a necessity. Depending on price and how hard it'll be we might look into a simple account area aswell so users can see past orders etc If this is easier build on other 3rd party ecommerce software i'm open to suggestions Thanks